Trane Cnt Svx07C En Users Manual ZN.521 Book File

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Installation and
Operation
Tracer™ ZN521
Zone Controller

CNT-SVX07C-EN

Installation and
Operation
Tracer™ ZN521
Zone Controller

CNT-SVX07C-EN
April 2005

CNT-SVX07C-EN

Tracer ZN521 Zone Controller Installation and Operation
This guide and the information in it are the property of American Standard Inc. and may not be used or reproduced in whole or in part,
without the written permission of American Standard Inc. Trane, a business of American Standard, Inc., has a policy of continuous
product and product data improvement and reserves the right to change design and specification without notice.
Although Trane has tested the hardware and software described in this guide, no guarantee is offered that the hardware and software
are error free.
Trane reserves the right to revise this publication at any time and to make changes to its content without obligation to notify any person of such revision or change.
Trane may have patents or patent applications covering items in this publication. By providing this document, Trane does not imply
giving license to these patents.

™®

The following are trademarks or registered trademarks of American Standard Inc.: Trane, Tracer, Rover.

™®

The following are trademarks or registered trademarks of their respective companies or organizations: BACnet from
ASHRAE; Neuron, LonMark, LonTalk, and LonWorks from Echelon Corporation; National Electrical Code form the National
Fire Proctection Association, Inc.

Printed in the U.S.A.
© 2005 American Standard Inc. All rights reserved

CNT-SVX07C-EN

NOTICE:
Warnings and Cautions appear at appropriate sections throughout this manual. Read these carefully:

WARNING
Indicates a potentially hazardous situation, which, if not avoided, could result in death or serious injury.

CAUTION
Indicates a potentially hazardous situation, which, if not avoided, may result in minor or moderate injury.
It may also be used to alert against unsafe practices.

CAUTION
Indicates a situation that may result in equipment damage or property damage.

The following format and symbol conventions appear at appropriate sections throughout this manual:

IMPORTANT
Alerts installer, servicer, or operator to potential actions that could cause the product or system to
operate improperly but will not likely result in potential for damage.
Note:
A note may be used to make the reader aware of useful information, to clarify a point, or to describe
options or alternatives.
◆

This symbol precedes a procedure that consists of only a single step.

CNT-SVX07C-EN

Contents
Chapter 1

Overview and specifications . . . . . . . . . . . . . . . . . . 1
Product description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Storage environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Clearances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Agency listing/compliance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Additional components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Power transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Water, duct, and outdoor-air temperature sensors . . . . . . . . . . . . . . 4
Binary input switching devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Output devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Zone temperature sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Valve actuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Damper actuators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Zone humidity sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
CO2 sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Chapter 2

General wiring information . . . . . . . . . . . . . . . . . . . 7
Input/output terminal wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
AC-power wiring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Communication-link wiring and addressing . . . . . . . . . . . . . . . . . . . . . . 9

Chapter 3

Mounting the controller . . . . . . . . . . . . . . . . . . . . 11
Location recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Operating environment requirements . . . . . . . . . . . . . . . . . . . . . . . . . . .11
Mounting recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Chapter 4

Input/output functions and wiring for typical
applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Binary inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
BI1: Low-coil-temperature detection . . . . . . . . . . . . . . . . . . . . . . . . 14
BI2: Condensate overflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
BI3: Occupancy or generic binary input . . . . . . . . . . . . . . . . . . . . . . 15
BI4: Fan status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

CNT-SVX07C-EN

Contents

Analog inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
GND: Ground terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
ZN: Zone temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
SET: Local setpoint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
FAN: Fan mode input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
AI1: Entering water temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
AI2: Discharge air temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
AI3: Outdoor air temperature or generic temperature . . . . . . . . . . 18
AI4: Universal 4–20 mA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Binary outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Generic binary output. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Overriding binary outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Wiring requirements and options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Chapter 5

Sequence of operations . . . . . . . . . . . . . . . . . . . . 35
Power-up sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Random start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Occupancy modes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Occupied mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Unoccupied mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Occupied standby mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
Occupied bypass mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Timed override control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Zone temperature control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Cascade zone control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Simplified zone control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Discharge air tempering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Morning warm-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Morning cool-down. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Heating or cooling mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Entering water temperature sampling function . . . . . . . . . . . . . . . . . . . 40
Fan operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Exhaust control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Valve operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Modulating valve operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Modulating valve calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Two-position valve operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Isolation-valve operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Two-pipe operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Four-pipe operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

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Contents

Modulating outdoor/return air dampers. . . . . . . . . . . . . . . . . . . . . . . . . 43
ASHRAE Cycle 1 conformance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
ASHRAE Cycle 2 conformance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Economizing (free cooling) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Two-position control of a modulating outdoor air damper . . . . . . . . . 46
Face-and-bypass damper operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Face-and-bypass, isolation-valve operation . . . . . . . . . . . . . . . . . . 46
DX cooling operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Electric heat operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Baseboard heat operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Dehumidification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Peer-to-peer communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Unit protection strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Smart reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Low-coil-temperature protection . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Condensate overflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Fan status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Fan off delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Filter-maintenance timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Freeze avoidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Freeze protection (discharge air temperature low limit) . . . . . . . . 50

Chapter 6

Status indicators for operation and
communication. . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Test button. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Manual output test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Service pin button. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Interpreting LEDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Types of diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Manual (latching) diagnostics. . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Automatic (nonlatching) diagnostics . . . . . . . . . . . . . . . . . . . . . 58
Smart reset diagnostics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Informational diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Table of diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

CNT-SVX07C-EN

iii

Contents

Chapter 7

Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

CNT-SVX07C-EN

Chapter 1

Overview and specifications
This guide provides installation and configuration information for the
Tracer ZN521 zone controller, as well as a description of its operations.
The overview includes a product description, specifications, and descriptions of ancillary products that may be necessary.

Product description
The Tracer ZN521 is an application-specific controller that provides
direct-digital zone temperature control. The controller can operate as a
stand-alone device or as part of a building automation system (BAS).
Communication between the controller and a BAS occurs by means of a
LonTalk communication link, which complies with the LonTalk protocol.
The Tracer ZN521 supports the following equipment:

•
•
•

Fan coils
Unit ventilators
Blower coils

The Tracer ZN521 can be configured to control:

•
•
•
•

Tri-state modulating or two-position valves
Tri-state modulating dampers:
outdoor/return air, and face-and-bypass
DX cooling (single stage)
Electric heat (two stages)

It is designed to be field-installed and is sent from the factory unconfigured. Use the PC-based Rover service tool to configure the controller for
specific applications
Note:
For information about using the Rover service tool, see the
Rover Installation/Operation/Programming guide (EMTXSVX01A-EN).

CNT-SVX07C-EN

Chapter 1 Overview and specifications

Storage environment
If a Tracer ZN521 zone controller is to be stored for a substantial amount
of time, store it in an indoor environment that meets the following
requirements:
•
•

Temperature: –40° to 185°F (–40° to 85°C)
Relative humidity: 5–95%, noncondensing

Dimensions
Plastic-cover model dimensions
For complete dimensional drawing, see Figure 1 on page 3.

•
•
•

Height: 5.375 in. (137 mm)
Width: 6.875 in. (175 mm)
Depth: 2 in. (51 mm)

Metal-cover model dimensions
For complete dimensional drawing, see Figure 2 on page 3.

•
•
•

Height: 9.0 in (25 mm)
Width: 10.37in. (263 mm)
Depth: 2.25 in. (58 mm)

Clearances
Plastic-cover model
(see Figure 1 on page 3)

•
•
•

Front: 4.0 in. (102 mm)
Each side: 1.0 in. (25 mm)
Top and bottom: 4.0 in. (102 mm)

Metal-cover model
(see Figure 2 on page 3)

•
•
•

Front: 24.0 in. (610 mm)
Each side: 2.0 in. (51 mm)
Top and bottom: 1.0 in. (25 mm)

CNT-SVX07C-EN

Clearances

Figure 1. Plastic-cover model dimensions and clearances
1 in
(25 mm)

4 in
(102 mm)

4 in.
(102 mm)

5.625 in.
(143 mm)

6.31
(160 mm)

4 in
(102 mm)

6.875 in
(175 mm)

5.625 in (143 mm)
2 in. (51 mm)

1 in
(25 mm)

Figure 2. Metal-cover model dimensions and clearances
1 in.
(25 mm)

1.875 in.
(48 mm)

6.5 in.
(165 mm)
0.28 in.
(7 mm)

9 in.
(229 mm)
9 in.
(229 mm)

7 in.
(178 mm)
2 in.
(51 mm)

2 in.
(51 mm)

24 in.
(610 mm)

10.37 in.
(263 mm)
width with cover

Clearances
Dimensions

CNT-SVX07C-EN

1 in.
(25 mm)

1 in.
(25 mm)
2.25in.
(58 mm)

10.25 in.
(260 mm)
width without cover

Chapter 1 Overview and specifications

Agency listing/compliance
CE—Immunity: EN 50082-1:1997; EN 50082-2:1995
CE—Emissions: EN 50081-1:1992 (CISPR 22) Class B
UL and C-UL 916 listed: Energy management system
UL 94-5V (UL flammability rating for plenum use)
FCC Part 15, Class A
ASHRAE Cycle 1 & Cycle 2 control sequences

Additional components
The Tracer ZN521 zone controller requires the use of additional components for monitoring and proper control of the associated equipment. The
use of specific components depends on the application. These components
are not included with the Tracer ZN521 zone controller.

Power transformer
Use a UL-listed Class 2 power transformer supplying a nominal 24 Vac
(19–30 Vac) to power both the Tracer ZN521 zone controller (14 VA) and
its associated output devices, including relays and actuators, to a maximum of 12 VA per output utilized.

Water, duct, and outdoor-air temperature sensors
Temperature sensors must be Trane 10 kΩ (at 25°C) thermistors. Entering water and discharge air inputs may use a sealed temperature sensor
(part number 4190 1100).

Binary input switching devices
Occupancy, condensate overflow, low-coil-temperature, and fan status
inputs accept switching devices that may have normally open or normally
closed dry contacts.

Output devices
Output devices connected to the Tracer ZN521 binary outputs cannot
exceed 12 VA (0.5 A) current draw at 24 Vac.

Zone temperature sensors
Table 1 shows the Trane zone temperature sensors that are supported by
the Tracer ZN521 zone controller.

Valve actuators
Valve actuators cannot exceed 12 VA draw at 24 Vac. For two-position
valves, use actuators with on/off action, and with a spring action that

CNT-SVX07C-EN

Additional components

Table 1. Tracer zone temperature sensor options
Fan
BAS
order
number

Timed
override
buttons

Zone

Comm
jack

Use
High

Med

Low

Auto

Off

Setpoint
thumbwheel

Temperature
sensor

Cancel

4190 1087

Any

4190 1088

Any

4190 1090

Any

4190 1094

Any

4190 1095

Unit
ventilator

4190 1115

Fan coil

4190 1116

Unit
ventilator

4190 1117

Any

x
x

returns the valve to normally open or closed (dependent on the desired
default position). For modulating valve control, use tri-state modulating
actuators with or without a spring return, as required by the application.

Damper actuators
Damper actuators cannot exceed 12 VA draw at 24 Vac. For control of outdoor/return air dampers, use tri-state modulating actuators that incorporate a spring return.

Zone humidity sensor
For measurement of relative humidity (RH), the Tracer ZN521 requires a
zone humidity sensor with a 4–20 mA output, where 4 mA is 0% RH and
20 mA is 100% RH. The controller provides 20 Vdc to power the zone
humidity sensor.

CO2 sensor
For CO2 measurement, the Tracer ZN521 requires a CO2 sensor with a 4–
20 mA output, where 4 mA = 0 ppm and 20 mA = 2000 ppm.

CNT-SVX07C-EN

Chapter 1 Overview and specifications

CNT-SVX07C-EN

Chapter 2

General wiring information
This chapter provides specifications and general information about wiring the Tracer ZN521 zone controller. The controller requires wiring for:

•
•
•

Input/output terminals
AC power to the controller
Communication-link wiring, if the controller is to communicate with a
building automation system (BAS)

Input/output terminal wiring
All input/output terminal wiring for the Tracer ZN521 zone controller is
application specific and dependant on the configuration of the controller.
Input/output terminal wiring must meet the following requirements:

•
•
•
•
•

All wiring must comply with the National Electrical Code and local
codes.
Use only 18 AWG, twisted-pair wire with stranded, tinned-copper
conductors. (Shielded wire is recommended.)
Binary input and output wiring must not exceed 1000 ft (300 m).
Analog input wiring must not exceed 300 ft (100 m).
Do not run input/output wires in the same wire bundle with any acpower wires.

For application-specific wiring information and diagrams, see Chapter 4,
“Input/output functions and wiring for typical applications”

AC-power wiring
WARNING
HAZARDOUS VOLTAGE!
Before making line voltage electrical connections, lock open the supplypower disconnect switch. Failure to do so may cause death or serious
injury.

CAUTION
Make sure that the 24 Vac transformer is properly grounded. Failure to
do so may result in damage to equipment and/or personal injury.

CNT-SVX07C-EN

Chapter 2 General wiring information

CAUTION
Complete input/output wiring before applying power to the Tracer
ZN521 zone controller. Failure to do so may cause damage to the controller or power transformer due to inadvertent connections to power
circuits.

IMPORTANT
Do not share 24 Vac between controllers.
All wiring must comply with National Electrical Code and local codes.
The ac-power connections are in the top left corner of the Tracer ZN521
zone controller (see Figure 3).
Figure 3. Connecting ac-power wires to the controller

H
24 Vac
transformer

The Tracer ZN521 may be powered by an existing transformer integral to
the controlled equipment, provided the transformer has adequate power
available and proper grounding is observed. If you are providing a new
transformer for power, use a UL-listed Class 2 power transformer supplying a nominal 24 Vac (19–30 Vac). The transformer must be sized to provide adequate power to both the Tracer ZN521 zone controller (14 VA)
and its associated output devices, including relays and actuators, to a
maximum of 12 VA per output utilized.

CNT-SVX07C-EN

Communication-link wiring and addressing

Communication-link wiring and
addressing
The Tracer ZN521 zone controller communicates with the BAS and with
other LonTalk controllers by means of a LonTalk communication link.

IMPORTANT
For important instructions on network wiring, refer to the Tracer Summit Hardware and Software Installation guide (BMTX-SVN01A-EN).
Wiring for the communication link must meet the following requirements:

•
•
•

All wiring must comply with the National Electrical Code and local
codes.
22 AWG Level 4 unshielded communications wire recommended for
most Comm5 installations.
Termination resistors are required for wiring LonTalk devices communicating on a network. For specific information about using termination resistors for LonTalk applications, refer to the Tracer Summit
Hardware and Software Installation guide (BMTX-SVN01A-EN).

Each Tracer ZN521 zone controller has a unique 12-character alphanumeric device address for communicating on a BAS network. This address,
referred to as a Neuron ID, is assigned in the factory before the product is
shipped and cannot be changed. Each controller can be identified by viewing its unique Neuron ID, which is on a printed label attached to the circuit board of the controller. Additional adhesive-backed, peel-off Neuron
ID labels are tethered to the controller for placing on mechanical prints or
unit location worksheets. The Neuron ID will appear when communication is established with the Rover service tool or a BAS. An example Neuron ID is 00-01-64-1C-2B-00.

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Chapter 2 General wiring information

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Chapter 3

Mounting the controller
This chapter gives recommendations and requirements for mounting a
Tracer ZN521 zone controller.

Location recommendations
Trane recommends locating the Tracer ZN521 zone controller:

•
•
•

Near the controlled piece of equipment to reduce wiring costs
Where it is easily accessible for service personnel
Where public access is restricted to minimize the possibility of tampering or vandalism

The controller can often be mounted inside the wiring enclosure of the
associated mechanical equipment.

Operating environment requirements
Operate a Tracer ZN521 zone controller in an indoor environment that
meets the following requirements:
•
•

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Temperature: from 32°F to 140°F (from 0°C to 60°C)
Relative humidity: 5–95%, noncondensing

Chapter 3 Mounting the controller

Mounting recommendations
Mounting recommendations are as follows:

CAUTION
Mount the Tracer ZN521 zone controller with the cover on to avoid the
possibility of damaging the circuit board during installation.

•
•
•
•

Mount the controller in any position, other than with the front of the
cover facing downward.
Mount using the two 3/16 in. (4.8 mm) radius mounting holes provided
(see Figure 4). Mounting fasteners are not included.
Attach the controller securely so it can withstand vibrations of associated HVAC equipment.
When the controller is mounted in a small enclosed compartment,
complete all wiring connections before securing the controller in the
compartment.

Figure 4. Mounting the Tracer ZN521 zone controller

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Chapter 4

Input/output functions and
wiring for typical applications
This chapter provides information about the function of inputs and outputs and examples of wiring for typical applications. Applications supported by the Tracer ZN521 zone controller are shown in Table 2.

2-pipe hydronic cooling only

2-pipe hydronic heating only

2-pipe changeover

2-pipe steam only

4-pipe hydronic heating and cooling

4-pipe changeover

4-pipe steam/chilled water

Electric heat

Auxiliary (baseboard) heat

Economizing

Valve control

Face and bypass damper

Auto minimum damper adjust

Application

Dehumidification

Multiple fan speed

Table 2. Typical applications for the Tracer ZN521 zone controller

Electric heat only (single- and two-stage)

DX/hydronic heating

DX/steam heating

DX cooling only

x
x

Figures 7 through 17 (pages 23 through 33) show typical wiring diagrams
that include all required and all optional components for typical applications.

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Chapter 4 Input/output functions and wiring for typical applications

Binary inputs
The Tracer ZN521 controller includes four binary inputs. Each binary
input associates an input signal of 0 Vac with open contacts and 24 Vac
with closed contacts. You can use the Rover service tool to configure each
of the inputs as normally open or normally closed. If an application does
not warrant the use of a particular input, configure the input as Not
Used. This will disable the generation of diagnostics for this function.
Table 3 gives the function of each binary input.
Table 3. Binary inputs
Binary input
terminal label

Function

BI1

Low-coil-temperature detection

BI2

Condensate overflow

BI3

Occupancy or generic binary input

BI4

Fan status

Each function is explained in the following paragraphs. For an explanation of the diagnostics generated by each binary input, see “Diagnostics”
on page 58. For more information about how the controller operates, see
Chapter 5, “Sequence of operations”

BI1: Low-coil-temperature detection
Note:
BI1 applies to hydronic/steam coils only.
The function of low-coil-temperature detection is to protect the coil from
freezing. If BI1 is wired to a binary low-coil-temperature detection device
(freeze-protection switch) and a low-coil-temperature condition exists, the
Tracer ZN521 will detect the condition and generate a Low Coil Temp
Detection diagnostic.

BI2: Condensate overflow
The function of condensate overflow is to prevent the condensate drain
pan from overflowing and causing water damage to the building. If BI2 is
wired to a condensate overflow switch and the level of condensate reaches
the trip point, the Tracer ZN521 will detect the condition and generate a
Condensate Overflow diagnostic.

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Binary inputs

BI3: Occupancy or generic binary input
The BI3 binary input can function as either:

•
•

The occupancy input
A generic binary input

The function of occupancy is to save energy by spreading zone setpoints
when the zone is unoccupied. As the occupancy input, BI3 can be used for
two related functions. For stand-alone controllers, BI3 can be hard-wired
to a binary switch or timeclock to determine the occupancy mode—either
occupied or unoccupied. For controllers receiving a BAS-communicated
occupancy request, the function of BI3 is to change the mode from occupied to occupied standby. (For more information on occupancy-related
functions, see “Occupancy modes” on page 36.)
BI3 is the only binary input that can be configured as generic. If configured as a generic binary input, it can be monitored by a BAS and has no
direct effect on Tracer ZN521 operation.

BI4: Fan status
The fan status input provides feedback to the controller regarding the
fan’s operating status. If BI4 is wired to a fan status switch and the input
indicates that the fan is not operating when the controller has the fan
controlled to on, the controller will generate a Low AirFlow—Fan Failure
diagnostic. (For more information, see “Fan status” on page 49.)

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Chapter 4 Input/output functions and wiring for typical applications

Analog inputs
The Tracer ZN521 controller includes seven analog inputs. Table 4
describes their functions. Each function is explained in the following
paragraphs. For an explanation of the diagnostics generated by each analog input, see “Diagnostics” on page 58. For more information about how
the controller operates, see Chapter 5, “Sequence of operations”
Table 4. Analog inputs
Analog input
terminal label
ZN

Function
Zone temperature

GND

Zone sensor common ground

SET

Local setpoint

FAN

Fan mode input

GND

Auxiliary ground

AI1

Entering water temperature

AI2

Discharge air temperature

AI3

Outdoor air temperature or generic temperature

AI4

Universal 4–20 mA

GND: Ground terminals
Use a GND terminal as the common ground for all zone sensor analog
inputs.

ZN: Zone temperature
The ZN analog input functions as the local (hard-wired) zone temperature
input. The controller receives the temperature as a resistance signal from
a 10 kΩ thermistor in a standard Trane zone sensor wired to analog input
ZN. A zone temperature value communicated by means of a LonTalk link
can also be used for controllers operating on a BAS. When both a hardwired and communicated zone temperature value is present, the controller uses the communicated value. If neither a hard-wired nor a communicated zone temperature value is present, the controller generates a Zone
Temp Failure diagnostic.
The ZN analog input is also used to communicate timed override requests
and cancel requests to the controller for applications using a Trane zone
sensor with ON and CANCEL buttons.

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Analog inputs

SET: Local setpoint
The SET analog input functions as the local (hard-wired) temperature
setpoint input for applications utilizing a Trane zone sensor with a temperature setpoint thumbwheel. The local setpoint input is configurable
(as enabled or disabled) using the Rover service tool. A setpoint value
communicated by means of a LonTalk link can also be used for controllers
operating on a BAS. If both hard-wired and communicated setpoint values are present, the controller uses the communicated value. If neither a
hard-wired nor a communicated setpoint value is present, the controller
uses the stored default setpoints (configurable using the Rover service
tool). If a valid hard-wired or communicated setpoint value is established
and then is no longer present, the controller generates a Setpoint Failure
diagnostic.

FAN: Fan mode input
The FAN analog input functions as the local (hard-wired) fan mode
switch input for applications using the Trane zone sensor with a fan mode
switch option. The various fan mode switch positions (off, low, medium,
high, auto) provide different resistances that are interpreted by the
Tracer ZN521. The local fan mode switch input is configurable (as
enabled or disabled) using the Rover service tool. A communicated fan
mode request via the LonTalk communications link can also be used for
controllers operating on a BAS. If both hard-wired and communicated fan
mode values are present, the controller uses the communicated value. If
neither a hard-wired nor a communicated fan mode value is present, the
controller recognizes the fan mode value as auto and operates according
to the default configuration. If a valid hard-wired or communicated fan
mode value is established and then is no longer present, the controller
generates a Fan Mode Failure diagnostic.

AI1: Entering water temperature
The AI1 analog input functions as the local (hard-wired) entering water
temperature input. An entering water temperature communicated via the
LonTalk communications link can also be used for controllers operating
on a BAS. If both hard-wired and communicated entering water temperature values are present, the controller uses the communicated value. If a
valid hard-wired or communicated entering water temperature value is
established and then is no longer present, the controller generates an
Entering Water Temp Failure diagnostic.
For units configured as 2-pipe or 4-pipe changeover units, the entering
water temperature is used to make heating/cooling operation decisions. If
neither a hard-wired nor a communicated entering water temperature
value is present on changeover units, the controller will always operate in
heating mode.

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Chapter 4 Input/output functions and wiring for typical applications

For units not configured as changeover units, the entering water temperature value is used for information and troubleshooting only and does not
affect the operation of the controller.
Note:
AI1 is not polarity sensitive; you can connect either terminal to
either sensor lead.

AI2: Discharge air temperature
The AI2 analog input functions as the local discharge air temperature
input.

IMPORTANT
The Tracer ZN521 cannot operate without a valid discharge air temperature value.
The controller receives the temperature as a resistance signal from a
10 kΩ thermistor wired to analog input AI2. The thermistor is typically
located downstream from all unit heating and cooling coils at the unit discharge area.
If a discharge air temperature value is invalid or is not present, the controller generates a Discharge Air Temp Failure diagnostic and shuts
down the equipment. When the thermistor returns to a valid temperature, the controller automatically allows the equipment to resume normal
operation.
Note:
AI2 is not polarity sensitive; you can connect either terminal to
either sensor lead.

AI3: Outdoor air temperature or generic temperature
The AI3 analog input can function as either:

•
•

An outdoor air temperature input
A generic temperature input

If AI3 is configured as the local (hard-wired) outdoor air temperature
input, the controller receives the temperature as a resistance signal from
a 10 kΩ thermistor wired to analog input AI3. An outdoor air temperature value communicated by means of a LonTalk link can also be used for
controllers operating on a BAS. If both hard-wired and communicated
outdoor air temperature values are present, the controller uses the communicated value. If a valid hard-wired or communicated outdoor air temperature value is established and then is no longer present, the controller
generates an Outdoor Air Temp Failure diagnostic.

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Analog inputs

Economizing (free cooling) is a function whereby outdoor air is used as a
source of cooling before hydronic or DX cooling is used. The Tracer ZN521
uses the outdoor air temperature value to determine whether economizing is feasible. Economizing is not possible without a valid outdoor air
temperature. (For more information, see “Economizing (free cooling)” on
page 45.)
The outdoor air temperature value is also used for the freeze avoidance
function. This function is used for low-coil-temperature protection when
the fan is off. The controller enters the freeze avoidance mode when the
outdoor air temperature is below the freeze avoidance setpoint (configurable using the Rover service tool). (For more information, see “Freeze
avoidance” on page 50.)
If AI3 is configured as a generic temperature input, it can be monitored
by a BAS. The controller receives the temperature as a resistance signal
from a 10 kΩ thermistor wired to analog input AI3. The generic temperature input can be used with any Trane 10 kΩ thermistor. The thermistor
can be placed in any location and has no effect on the operation of the controller. The controller will generate a Generic Temperature Failure diagnostic if the input becomes invalid or goes out of range.
Note:
AI3 is not polarity sensitive; you can connect either terminal to
either sensor lead.

AI4: Universal 4–20 mA
The AI4 analog input can be configured in one of the three ways shown in
Table 5.
Table 5. AI4 configuration options and associated measurement ranges
Configuration

Measurement range

Generic 4–20 mA input

0–100%
(4 mA=0%; 20 mA=100%)

CO2 measurement

0–2000 ppm
(4 mA=0 ppm; 20 mA=2000 ppm)

Relative humidity (RH) measurement

0–100%
(4 mA=0% RH; 20 mA=100% RH)

If this input is not needed for an application, configure it as Not Used.
This will disable the generation of diagnostics.
Note:
AI4 is polarity sensitive.
For the generic input configuration, a 4–20 mA sensor must be hardwired to the AI4 terminal. (Wiring is dependent on the specific application.) The sensor communicates a value of 0–100% to the BAS. This configuration has no direct effect on Tracer ZN521 operation. If a valid value

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Chapter 4 Input/output functions and wiring for typical applications

is established and then is no longer present, the controller generates a
Generic AIP Failure diagnostic.
For the CO2 measurement configuration, a 4–20 mA sensor must be hardwired to the AI4 terminal as shown in Figure 5. The sensor will transmit
a 0–2000 ppm value to the BAS. This configuration has no direct effect on
Tracer ZN521 operation. If a valid value is established and then is no
longer present, the controller generates a CO2 Sensor Failure diagnostic.
Figure 5. AI4 terminal wiring: CO2 measurement
Tracer ZN521

24 Vac

CO2 sensor
(Trane 5010 0828 shown)

24 Vac
GND

Signal

For the RH measurement configuration, either a hard-wired 4–20 mA
zone humidity sensor (see Figure 6) must provide a value to the controller
or a BAS communicates a value to the controller. The controller uses this
value to support the dehumidification function. (For more information,
see “Dehumidification” on page 47.) If a valid hard-wired or communicated relative humidity value is established and then is no longer
present, the controller generates a Humidity Input Failure diagnostic and
disables the dehumidification function.
Figure 6. AI4 terminal wiring: RH measurement
Tracer ZN521

RH sensor

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Binary outputs

Binary outputs
The ZN521 zone controller supports fan coil, blower coil, and unit ventilator applications that may include the following components:

•
•
•
•
•
•
•

Supply fan with up to three speeds
Hydronic cooling and/or heating coils with two-position or tri-state
modulating control valve
DX cooling (single stage)
Electric heat (single stage or two stage)
Baseboard heat (single stage)
Tri-state modulating outdoor/return air damper
Tri-state modulating face-and-bypass damper

The Tracer ZN521 controller includes ten binary outputs. Each binary
output is a triac with a rating of 12 VA at 24 Vac. Table 6 describes the
function of each output.
Table 6: Binary output functions
Binary output

Functions

• Fan high

• Fan medium
• Exhaust fan or damper

• Fan low

• Modulating cooling/changeover valve, open
• Two-position cooling/changeover valve
• DX cooling

• Modulating cooling/changeover valve, close
• Face-and-bypass damper, open to face

• Modulating heating valve, open
• Two-position heating valve
• Electric heat, stage 1

• Modulating heating valve, close
• Face-and-bypass damper, close (bypass)
• Electric heat, stage 2

• Outdoor air damper, open (return air damper, close)

• Outdoor air damper, close (return air damper, open)

• Baseboard heat
• Generic

Generic binary output
Binary output 10 is the only output that can be configured as a generic
binary output. When configured as a generic binary output, it can be controlled only by a BAS, and has no direct effect on Tracer ZN521 operation.

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Chapter 4 Input/output functions and wiring for typical applications

Overriding binary outputs
The Tracer ZN521 controller includes a manual output test and a water
valve override feature. Use the manual output test to manually control
the outputs in a defined sequence. For information, see “Manual output
test” on page 52.
The water valve override feature is a procedure used for water balancing.
Using the Rover service tool or a BAS, a user can specify that a Tracer
ZN521 override the state of water valves to:

•
•

Open all valves
Close all valves

The controller resets itself to normal operation after two hours.

Wiring requirements and options
Table 7 shows required controller inputs for minimal proper operation of
all applications.
Table 7. Required controller inputs for proper operation
Function

Input source

For more information,
see:

24 Vac power

Terminals: GND, 24 V

“AC-power wiring” on
page 7

Zone temperature

Terminals: ZN, GND
or communicated

“ZN: Zone temperature” on page 16

Discharge air temperature

Terminals: AI2

“AI2: Discharge air temperature” on page 18

Entering water temperature—required only for
units with auto
changeover

Terminal: AI1
or communicated

“AI1: Entering water
temperature” on
page 17

Outdoor air temperature—
required only for economizing

Terminals: AI3 or
communicated

“AI3: Outdoor air temperature or generic
temperature” on
page 18

Relative humidity—
required only for dehumidification

Terminals: AI4

“AI4: Universal 4–
20 mA” on page 19

Figure 7 on page 23 through Figure 17 on page 33 show typical applications that include all required and all optional components.

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Wiring requirements and options

Figure 7. Two-pipe hydronic-cooling unit

Fan status (closed=on)*

24 V†
Fan, high speed
24 V†
Exhaust (or fan, medium speed)
24 V†
Fan, low speed
24 V†
Cooling valve

Occupancy (open=occupied)*

24 V†
Electric heat, stage 1 (optional)
24 V†
Electric heat, stage 2 (optional)

Condensate overflow (closed=normal)*

24 V†
Outdoor air damper actuator
Open
Close

24 Vac H
N

Open
Close

Low-coil-temperature detection
(closed=normal)*

24 V†
Generic/baseboard heat

LonTalk
AI4 input: See
Figures 5 and 6
on page 20 for
wiring options

LonTalk

Entering water
temperature
Discharge air
temperature

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in
out

Outdoor air or
generic temperature

* All binary inputs are configurable.
† Connect 24 V to an AC POWER (24V) terminal.

Chapter 4 Input/output functions and wiring for typical applications

Figure 8. Two-pipe hydronic-heating unit
24 V†
Fan, high speed
24 V†
Exhaust (or fan, medium speed)
24 V†
Fan, low speed
Fan status (closed=on)*
24 V†
Heating valve

Occupancy (open=occupied)*
Condensate overflow (closed=normal)*

24 V†
Outdoor air damper actuator
Open
Close

24 Vac H
N

Open
Close

Low-coil-temperature detection
(closed=normal)*

24 V†
Generic/baseboard heat

LonTalk
AI4 input: See
Figures 5 and 6
on page 20 for
wiring options

LonTalk

Entering water
temperature

in
out

Outdoor air or generic temperature

Discharge air
temperature

* All binary inputs are configurable.
† Connect 24 V to an AC POWER (24V) termi-

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Wiring requirements and options

Figure 9. Two-pipe hydronic heating/cooling unit with auto changeover

Fan status (closed=on)*

24 V†
Fan, high speed
24 V†
Exhaust (or fan, medium speed)
24 V†
Fan, low speed
24 V†
Heating/cooling changeover valve

Occupancy (open=occupied)*

24 V†
Electric heat, stage 1 (optional)
24 V†
Electric heat, stage 2 (optional)

Condensate overflow (closed=normal)*

24 V†
Outdoor air damper actuator
Open
Close

24 Vac H
N

AI4 input: See
Figures 5 and 6
on page 20 for
wiring options

LonTalk

Entering water
temperature

Open
Close

Low-coil-temperature detection
(closed=normal)*

24 V†
Generic/baseboard heat

LonTalk
in

out

Outdoor air or
generic temperature

Discharge air
temperature

* All binary inputs are configurable.
† Connect 24 V to an AC POWER (24V) terminal.

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Chapter 4 Input/output functions and wiring for typical applications

Figure 10. Four-pipe hydronic heating/cooling unit
24 V†
Fan, high speed
24 V†
Exhaust (or fan, medium speed)
24 V†
Fan, low speed
Fan status (closed=on)*
24 V†
Cooling valve
24 V†
Heating valve

Occupancy (open=occupied)*
Condensate overflow (closed=normal)*

24 V†
Outdoor air damper actuator
Open
Close

Open
Close

24 Vac H
N

Open
Close

Low-coil-temperature detection
(open=normal)*

24 V†
Generic/baseboard heat

LonTalk
AI4 input: See
Figures 5 and 6
on page 20 for
wiring options

LonTalk

Entering water
temperature

in
out

Outdoor air or
generic temperature

Discharge air
temperature

* All binary inputs are configurable.
† Connect 24 V to an AC POWER (24V) terminal.

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Wiring requirements and options

Figure 11. Four-pipe heating/cooling unit with auto changeover
24 V†
Fan, high speed
24 V†
Exhaust (or fan, medium speed)
24 V†
Fan, low speed
Fan status (closed=on)*
24 V†
Heating/cooling changeover valve

Occupancy (open=occupied)*

24 V†
Auxiliary heating valve

Condensate overflow (closed=normal)*

24 V†
Outdoor air damper actuator
Open
Close

H
N

Open
Close

24 Vac

Open
Close

Low-coil-temperature detection
(closed=normal)*

24 V†
Generic/baseboard heat

LonTalk
AI4 input: See
Figures 5 and 6
on page 20 for
wiring options

LonTalk

Entering water
temperature

in
out

Outdoor air or
generic temperature

Discharge air
temperature

* All binary inputs are configurable.
† Connect 24 V to an AC POWER (24V) terminal.

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Chapter 4 Input/output functions and wiring for typical applications

Figure 12. Two-pipe heating unit with DX cooling
24 V†
Fan, high speed
24 V†
Exhaust (or fan, medium speed)
24 V†
Fan, low speed
Fan status (closed=on)*

24 V†
DX cooling

Occupancy (open=occupied)*
24 V†
Heating valve

Condensate overflow (closed=normal)*

24 V†
Outdoor air damper actuator

GND 24V 24V 24V

AC POWER

SERVICE
LED
PIN

BI1

BI2

BI3

BI4

BINARY INPUTS

ZONE SENSOR
ZN GND SET FAN GND

Open
Close

24 Vac H
N

Open
Close

Low-coil-temperature detection
(closed=normal)*

COMM5
LED

BINARY OUTPUTS

ANALOG INPUTS
AI1

AI2

AI3

COMM5
+20 AI4 GND

24 V†
Generic/baseboard heat

STATUS
LED

}
AI4 input: See
Figures 5 and 6
on page 20 for
wiring options

1
2
On

Cancel

LonTalk
in
out

3
4
5 LonTalk
6

Entering water
temperature

Outdoor air or generic temperature

Discharge air
temperature

* All binary inputs are configurable.
† Connect 24 V to an AC POWER (24V) terminal.

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Wiring requirements and options

Figure 13. Electric heat unit with DX cooling
24 V†
Fan, high speed
24 V†
Exhaust
Fan status (closed=on)*

24 V†
DX cooling

Occupancy (open=occupied)*

24 V†
Electric heat, stage 1 (optional)
24 V†
Electric heat, stage 2 (optional)
24 V†
Outdoor air damper actuator

Condensate overflow (closed=normal)*
Low-coil-temperature detection
(closed=normal)*

24 V†
Generic/baseboard heat

Open
Close

24 Vac H
N

GND 24V 24V 24V

AC POWER

SERVICE
LED
PIN

BI1

BI2

BI3

BI4

BINARY INPUTS

ZONE SENSOR
ZN GND SET FAN GND

ANALOG INPUTS
AI1

AI2

AI3

}

1
On

Cancel

COMM5
LED

COMM5
+20 AI4 GND

AI4 input: See
Figures 5 and 6
on page 20 for
wiring options

BINARY OUTPUTS

STATUS
LED

LonTalk
in

out

3
4
5
6

LonTalk

Entering water
temperature

Outdoor air or
generic temperature

Discharge air
temperature

* All binary inputs are configurable.
† Connect 24 V to an AC POWER (24V) terminal.

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Chapter 4 Input/output functions and wiring for typical applications

Figure 14. Electric heat unit
24 V†
Fan, high speed
24 V†
Exhaust
Fan status (closed=on)*
Occupancy (open=occupied)*

24 V†
Electric heat, stage 1
24 V†
Electric heat, stage 2
24 V†
Outdoor air damper actuator

Condensate overflow (closed=normal)*
Low-coil-temperature detection
(closed=normal)*
H
N

Open
Close

24 Vac

24 V†
Generic/baseboard heat

LonTalk
AI4 input: See
Figures 5 and 6
on page 20 for
wiring options

LonTalk

Entering water
temperature
Discharge air
temperature

in
out

Outdoor air or
generic temperature

* All binary inputs are configurable.
† Connect 24 V to an AC POWER (24V) terminal.

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Wiring requirements and options

Figure 15. Two-pipe heating unit with face-and-bypass damper
24 V†
Fan, high speed
24 V†
Exhaust (or fan, medium speed)
24 V†
Fan, low speed
Fan status (closed=on)*
24 V†
Face & bypass damper actuator

Occupancy (open=occupied)*
Condensate overflow (closed=normal)*

24 V†
Heat isolation valve, open/close
24 V†
Outdoor air damper actuator
Open
Close

Open

24 Vac H
N

Low-coil-temperature detection
(closed=normal)*

24 V†
Generic/baseboard heat

LonTalk
AI4 input: See
Figures 5 and 6
on page 20 for
wiring options

LonTalk

Entering water
temperature

in
out

Outdoor air or
generic temperature

Discharge air
temperature

* All binary inputs are configurable.
† Connect 24 V to an AC POWER (24V) terminal.

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Chapter 4 Input/output functions and wiring for typical applications

Figure 16. Two-pipe heating/cooling unit with face-and-bypass damper
24 V†
Fan, high speed
24 V†
Exhaust (or fan, medium speed)
Fan status (closed=on)*

24 V†
Fan, low speed
24 V†
Heating/cooling isolation valve, open/close

Occupancy (open=occupied)*

Open

24 Vac H
N

Low-coil-temperature detection
(closed=normal)*

Open
Close

24 V†
Face-and-bypass damper actuator
24 V†
Outdoor air damper actuator

Condensate overflow (closed=normal)*

24 V†
Generic/baseboard heat

LonTalk
AI4 input: See
Figures 5 and 6
on page 20 for
wiring options

LonTalk

Entering water
temperature

in
out

Outdoor air or
generic temperature

Discharge air
temperature

* All binary inputs are configurable.
† Connect 24 V to an AC POWER (24V) terminal.

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Wiring requirements and options

Figure 17. Four-pipe heating/cooling unit with face-and-bypass damper
24 V†
Fan, high speed

24 V†
Exhaust (or fan, medium speed)
24 V†
Fan, low speed

Fan status (closed=on)*
Occupancy (open=occupied)*

24 V†
Cooling isolation valve, open/close
24 V†
Face and bypass damper actuator

Condensate overflow (closed=normal)*

24 V†
Heating isolation valve, open/close
24 V†
Outdoor air damper actuator
Open
Close

H
N

Open

24 Vac

Low-coil-temperature detection
(closed=normal)*

24 V†
Generic/baseboard heat

LonTalk
AI4 input: See
Figures 5 and 6
on page 20 for
wiring options

LonTalk

Entering water
temperature
Discharge air
temperature

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in
out

Outdoor air or
generic temperature

* All binary inputs are configurable.
† Connect 24 V to an AC POWER (24V) terminal.

Chapter 4 Input/output functions and wiring for typical applications

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Chapter 5

Sequence of operations
The Tracer ZN521 zone controller will operate to maintain the zone temperature setpoint. This chapter discusses many of the operational
sequences used by the controller to accomplish this goal.

Power-up sequence
When 24 Vac power is initially applied to the Tracer ZN521 zone controller, the following sequence occurs:
1. The green status indicator LED turns on (see “Interpreting LEDs” on
page 56).
2. All outputs are controlled off. All modulating valves and dampers
close, and the face-and-bypass damper calibrates to bypass (when
present).
3. The controller reads all input local values to determine initial values.
4. The random-start timer begins (see “Random start” on page 35).
5. If a hard-wired zone-temperature value is not detected, the controller
begins to wait for a communicated value. (This can take several minutes [15-minute default] and occurs concurrently with the remainder
of the power-up sequence.)
6. The random-start timer expires.
7. The power-up control wait function begins automatically if the configured power-up control wait time is greater than 0 seconds. When this
function is enabled, the controller waits for the configured amount of
time (from 0 to 120 seconds) to allow a communicated occupancy
request to arrive. If a communicated occupancy request arrives, normal operation can begin. If a communicated occupancy request does
not arrive, the controller assumes stand-alone operation.
8. Normal operation begins assuming no diagnostics have been
generated.

Random start
Random start is intended to prevent all units in a building from energizing at the same time. The random-start timer delays the fan and any
heating or cooling start-up from 5 to 30 seconds. If neither heating nor
cooling is initiated, or if fan operation is not required during the delay, the
random-start timer will time-out.

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Chapter 5 Sequence of operations

Occupancy modes
Occupancy modes can be controlled by any of the following:

•
•
•
•

The state of the local (hard-wired) occupancy binary input BI3 (see
“BI3: Occupancy or generic binary input” on page 15)
A timed override request from a Trane zone sensor (see “Timed override control” on page 37)
A communicated signal from a peer device (see “Peer-to-peer communication” on page 48)
A communicated signal from a BAS

A communicated request, either from a BAS or a peer controller, takes
precedence over local requests. If a communicated occupancy request has
been established and is no longer present, the controller reverts to the
default (occupied) occupancy mode after 15 minutes (if no hard-wired
occupancy request exists). The Tracer ZN521 has the following occupancy
mode options:

•
•
•
•

Occupied
Unoccupied
Occupied standby
Occupied bypass

Occupied mode
In occupied mode, the controller maintains the zone temperature based
on the occupied heating or cooling setpoints. The controller uses the occupied mode as a default mode when other forms of occupancy request are
not present. The fan will run as configured (continuous or cycling). The
outdoor air damper will close when the fan is off. The temperature setpoints can be local (hard-wired), communicated, or stored default values
(configurable using the Rover service tool).

Unoccupied mode
In unoccupied mode, the controller attempts to maintain the zone temperature based on the unoccupied heating or cooling setpoint. The fan will
cycle between high speed and off. The outdoor air damper will remain
closed, unless economizing. The controller always uses the stored default
setpoint values (configurable using the Rover service tool), regardless of
the presence of a hard-wired or communicated setpoint value.

Occupied standby mode
The controller is placed in occupied standby mode only when a communicated occupied request is combined with an unoccupied request from
occupancy binary input BI3. In occupied standby mode, the controller
maintains the zone temperature based on the occupied standby heating
or cooling setpoints. Because the occupied standby setpoints are typically
spread 2°F (1.1°C) in either direction and the outdoor air damper is
closed, this mode reduces the demand for heating and cooling the space.

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Timed override control

The fan will run as configured (continuous or cycling) for occupied mode.
The controller always uses the stored default setpoint values (configurable using the Rover service tool), regardless of hard-wired or communicated setpoint values. In addition, the outdoor air damper uses the
Economizer Occupied Standby Minimum Position setpoint to reduce the
ventilation rate.

Occupied bypass mode
The controller is placed in occupied bypass mode when the controller is
operating in the unoccupied mode and either the timed override ON button on the Trane zone sensor is pressed or the controller receives a communicated occupied bypass signal from a BAS. In occupied bypass mode,
the controller maintains the zone temperature based on the occupied
heating or cooling setpoints. The fan will run as configured (continuous or
cycling). The outdoor air damper will close when the fan is off. The controller will remain in occupied bypass mode until either the CANCEL button is pressed on the Trane zone sensor or the occupied bypass time
(configurable using the Rover service tool) expires. The temperature setpoints can be local (hard-wired), communicated, or stored default values
(also configurable using the Rover service tool).

Timed override control
If the zone sensor has a timed override option (ON/CANCEL buttons), pushing the ON button initiates a timed override on request. A timed override
on request changes the occupancy mode from unoccupied mode to occupied bypass mode. In occupied bypass mode, the controller controls the
zone temperature based on the occupied heating or cooling setpoints. The
occupied bypass time, which resides in the Tracer ZN521 and defines the
duration of the override, is configurable from 0 to 240 minutes (default
value of 120 minutes). When the occupied bypass time expires, the unit
transitions from occupied bypass mode to unoccupied mode. Pushing the
CANCEL button cancels the timed override request. A timed override cancel request will end the timed override before the occupied bypass time
has expired and will transition the unit from occupied bypass mode to
unoccupied mode.
If the controller is in any mode other than unoccupied when the ON button is pressed, the controller still starts the occupied bypass timer without changing the mode to occupied bypass. If the controller is placed in
unoccupied mode before the occupied bypass timer expires, the controller
will be placed in occupied bypass mode and remain in that mode until
either the CANCEL button is pressed on the Trane zone sensor or the occupied bypass time expires.

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Chapter 5 Sequence of operations

Zone temperature control
The Tracer ZN521 zone controller uses two methods of zone temperature
control:

•
•

Cascade zone control—used in the occupied, occupied bypass, and
occupied standby modes
Simplified zone control—used in the unoccupied mode

Cascade zone control
Cascade zone control maintains zone temperature by controlling the discharge air temperature to control the zone temperature. The controller
uses the difference between the measured zone temperature and the
active zone temperature setpoint to produce a discharge air temperature
setpoint. The controller compares the discharge air temperature setpoint
with the discharge air temperature and calculates a unit heating/cooling
capacity accordingly (see Figure 18). The end devices (outdoor air damper,
valves, etc.) operate in sequence based on the unit heating/cooling capacity (0–100%).
Figure 18. Cascade zone control
Active zone
temperature
setpoint

Difference

Calculated
discharge air
temperature
setpoint

Measured
zone
temperature

Difference

Calculated unit
heating/cooling
capacity

Measured
discharge air
temperature

If the discharge air temperature falls below the Discharge Air Control
Point Low Limit (configurable using the Rover service tool) and cooling
capacity is at a minimum, available heating capacity will be used to raise
the discharge air temperature to the low limit (see “Discharge air tempering” on page 39).

Simplified zone control
In the unoccupied mode, the controller maintains the zone temperature
by calculating the required heating or cooling capacity (0–100%) according to the measured zone temperature and the active zone temperature
setpoint. The active zone temperature setpoint is determined by the current operating modes, which include occupancy and heat/cool modes.

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Discharge air tempering

Discharge air tempering
If the controller is in cooling mode, cascade zone control initiates a discharge air tempering function when the discharge air temperature falls
below the Discharge Air Control Point Low Limit (configurable using the
Rover service tool) and all cooling capacity is at a minimum. The discharge air tempering function allows the controller to provide heating
capacity (if available) to raise the discharge air temperature to the Discharge Air Control Point Low Limit.
The discharge air tempering function is often initiated under the following circumstances: Cold outdoor air is brought in through the outdoor air
damper when the damper is at (a high) minimum position, causing the
discharge air temperature to fall below the Discharge Air Control Point
Low Limit.

Morning warm-up
The morning warm-up feature is initiated when the controller is in transition from unoccupied to occupied mode and the zone temperature is 3°F
(1.7°C) below the occupied heating setpoint. The fan will be turned on and
the outdoor air damper will remain closed. The damper modulates
between closed and minimum position when the zone temperature is
2–3°F (1.2–1.7°C) below the active heating setpoint. When the zone temperature reaches the occupied heating setpoint, the controller begins
operating in the occupied mode.

Morning cool-down
The morning cool-down feature is initiated when the controller is in transition from unoccupied to occupied and the zone temperature is 3°F
(1.7°C) above the occupied heating setpoint. The fan will be turned on and
the outdoor air damper will remain closed. The damper modulates
between closed and minimum position when the zone temperature is
2–3°F (1.2–1.7°C) above the active cooling setpoint. When the zone temperature reaches the occupied heating setpoint, the controller begins
operating in the occupied mode.

Heating or cooling mode
The heating or cooling mode can be determined in one of two ways:

•
•

By a communicated signal from a BAS or a peer controller
Automatically, as determined by the controller

A communicated heating signal permits the controller to heat only. A
communicated cooling signal permits the controller to cool only. A communicated auto signal allows the controller to automatically change from
heating to cooling and vice versa.

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Chapter 5 Sequence of operations

In heating and cooling mode, the controller maintains the zone temperature based on the active heating setpoint and the active cooling setpoint,
respectively. The active heating and cooling setpoints are determined by
the occupancy mode of the controller.
For two-pipe and four-pipe changeover units, normal heat/cool operation
will not begin until the ability to conduct the desired heating or cooling
operation is verified. This is done using the entering water temperature
sampling function, for which a valid entering water temperature is
required. When neither a hard-wired nor a communicated entering water
temperature value is present on changeover units, the controller will
operate in heating mode only and assume the coil water is hot. The sampling function is not used.
The entering water temperature sampling function is used only for
changeover applications. It is used for information and troubleshooting
only and does not affect the operation of the controller. (For more information, see “Entering water temperature sampling function.”)

Entering water temperature sampling
function
The entering water temperature sampling function is used with two-pipe
and four-pipe changeover units and requires a valid entering water temperature value. If the entering water temperature value is less than 5°F
(2.8°C) above a valid zone temperature value for hydronic heating and
greater than 5°F (2.8°C) below a valid zone temperature value for
hydronic cooling, the sampling function is enabled. When the sampling
function is enabled, the controller opens the main hydronic valve to allow
the water temperature to stabilize. After 3 minutes, the controller again
compares the entering water temperature value to the zone temperature
value to determine if the desired heating or cooling function can be
accomplished. If the entering water temperature value remains out of
range to accomplish the desired heating/cooling function, the controller
closes the main hydronic valve and waits 60 minutes to attempt another
sampling. If the entering water temperature value falls within the
required range, it resumes normal heating/cooling operation and disables
the sampling function.

Fan operation
The Tracer ZN521 supports up to three fan speeds. Every time the fan is
enabled, the fan will begin operation and run on high speed for a period of
time (0.5 seconds for fan coils and 3 seconds for unit ventilators and
blower coils) before changing to any other speed. This is done to provide
adequate torque to start the fan motor from the off position. The fan will
always operate continuously while either heating or cooling during occupied, occupied standby, and occupied bypass operation. During unoccupied operation, the fan will cycle between off and high regardless of the

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Exhaust control

fan configuration. The controller can be configured to auto, to a specific
fan speed, or to off. If both a communicated and hard-wired value (fanspeed switch) is present, the communicated value has priority.
Note:
In occupied mode, The Tracer ZN521 zone controller requires
continuous fan operation because of cascade zone control. In
unoccupied mode, the fan cycles.
When the controller receives a communicated auto signal (or the associated fan-speed switch is set to AUTO with no communicated value
present), the fan will operate in the auto mode. In the auto mode, the fan
will operate according to the fan default (configurable using the Rover
service tool). The fan speed can be configured to default to auto, a specific
speed, or off for both heating and cooling operation.
Configured as auto and with multiple speeds available, the fan will automatically switch speeds depending on the difference between the zone
temperature and the active zone temperature setpoint. The fan speed will
increase as the difference increases and decrease as the difference
decreases.
When the controller receives a communicated fan-speed signal (high,
medium, low) or the associated fan-speed switch is set to a specific fan
speed, the fan will run continuously at the desired fan speed during occupied, occupied standby, and occupied bypass operation. During unoccupied operation, the fan will cycle between off and high regardless of the
communicated fan-speed signal or fan-speed switch setting (unless either
of these is off, which will control the fan off).
The fan will turn off when the controller receives a communicated off signal, when the fan-speed switch is set to OFF, when specific diagnostics are
generated, or when the default fan speed is set to off and the fan is operating in the auto mode.
The ability to enable or disable the controller’s associated fan speed
switch is configurable.

Exhaust control
Exhaust control is accomplished by a single-speed exhaust fan or a twoposition exhaust damper. BOP2 controls this function. To enable exhaust
control, configure the controller by selecting Exhaust Fan/Damper
Present and by selecting the number of fan speeds as either One or Two.
The exhaust function is coordinated with the supply fan and outdoor/
return air dampers as follows:

•

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The exhaust output is energized only when the supply fan is operating and the outdoor air damper position (%) is greater than or equal
to the Exhaust Fan/Damper Enable Setpoint (configurable using the
Rover service tool).

Chapter 5 Sequence of operations

•
•

The exhaust output is de-energized if the outdoor air damper position
drops 10% below the Exhaust Fan/Damper Enable Setpoint.
If the Exhaust Fan/Damper Enable Setpoint is less than 10%, the
exhaust output is energized if the outdoor air damper position is at
the setpoint and de-energized at 0.

Valve operation
The Tracer ZN521 zone controller supports one or two tri-state modulating or two-position valves, depending on the application (see Table 8). The
controller opens and closes the appropriate valve(s) to maintain the active
zone temperature setpoint at the heating setpoint in heating mode or the
cooling setpoint in cooling mode (see “Cascade zone control” on page 38).
For face-and-bypass applications, one or two isolation valves are
controlled.
Table 8. Valve control options
Tri-state
modulating

Two-position

Hydronic/steam fan coils and blower coils

Unit ventilators with valve control

Application

Face-and-bypass unit ventilators

Isolation
(two-position)

Modulating valve operation
The Tracer ZN521 supports tri-state modulating valve control. Two
binary outputs control each valve: one to drive the valve open and one to
drive the valve closed. The stroke time for each valve is configurable
using the Rover service tool. The controller supports heating, cooling, or
heat/cool changeover with a single valve/coil for two-pipe applications.
The controller supports cooling or heat/cool changeover with the main
valve/coil and heating only with the auxiliary valve/coil for four-pipe
applications. The controller moves the modulating valve to the desired
positions based on heating or cooling requirements.

Modulating valve calibration
Calibration of modulating valves is done automatically. During normal
operation, the controller overdrives the actuator (135% of the stroke time)
whenever a position of 0% or 100% is requested. as part of Tracer ZN521
normal operation. At power-up or after a power outage, the controller first
drives all modulating valves (and dampers) to the closed position. The
controller calibrates to the fully closed position by overdriving the actuator (135% of the stroke time). Then, the controller resumes normal
operation.

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Modulating outdoor/return air dampers

Two-position valve operation
The Tracer ZN521 supports two-position valves with a single binary output for each valve. Controllers used for two-pipe applications support
heating, cooling, or heat/cool changeover with a single valve/coil. Controller used for four-pipe applications support cooling or heat/cool changeover
with a main valve/coil, and heating only with an auxiliary valve/coil.

Isolation-valve operation
See “Face-and-bypass damper operation” on page 46.

Two-pipe operation
For two-pipe applications, the Tracer ZN521 can be configured as heating
only, cooling only, or heat/cool changeover. The coil can be used as the primary heating source and/or the primary cooling source. If present, an
electric heating element can be used only as the primary heating source
(instead of hydronic or steam heating). A changeover unit requires a valid
entering water temperature value—either communicated or hard-wired—
to operate properly (see “AI1: Entering water temperature” on page 17
and “Entering water temperature sampling function” on page 40).

Four-pipe operation
For four-pipe applications, the Tracer ZN521 can be configured as heat/
cool or heat/cool changeover. The main coil can be used as the primary
cooling source or the primary heating/cooling source. The auxiliary coil
can be used only as the primary heating source, not as a second stage of
heating. During normal operation, the controller never uses the main coil
and auxiliary coil simultaneously. A changeover unit requires a valid
entering water temperature value—either communicated or hard-wired—
to operate properly (see“AI1: Entering water temperature” on page 17
and “Entering water temperature sampling function” on page 40). Electric heat control is not available on four-pipe applications.

Modulating outdoor/return air dampers
The Tracer ZN521 operates the modulating outdoor/return air dampers
according to the following factors:

•
•
•
•
•
•

Occupancy mode
Outdoor air temperature (communicated or hard-wired sensor)
Zone temperature
Setpoint
Discharge air temperature
Discharge air temperature setpoint

The minimum position for an outdoor air damper is configurable using
the Rover service tool for occupied and occupied standby modes and for

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Chapter 5 Sequence of operations

low-speed fan operation. A controller can also receive a BAS-communicated outdoor air damper minimum position.
A BAS-communicated minimum position setpoint has priority over all
locally configured setpoints. When a communicated minimum position
setpoint is not present, the controller uses the configured minimum position for low fan speed whenever the fan is running at low speed, regardless of the occupancy state. See Table 9 and Table 10 for more information
about how the controller determines the position of the modulating outdoor air damper.
Table 9. Modulating outdoor air damper position setpoint determination
Occupancy

BAS-communicated
setpoint

Fan speed

Active minimum setpoint

Unoccupied

Any value

0% (closed)

Occupied
Occupied bypass
Occupied standby

Valid

Any value

BAS-communicated

Occupied
Occupied bypass
Occupied standby

Invalid

Low

Occupied low fan minimum

Occupied
Occupied bypass

Invalid

Medium/high

Occupied minimum

Occupied standby

Invalid

Medium/high

Occupied standby minimum

Table 10. Relationship between outdoor temperature sensors and damper position
Modulating outdoor air damper position
Outdoor air temperature
Occupied or occupied
bypass

Occupied standby

Unoccupied

No or invalid outdoor air
temperature

Open to occupied
minimum position

Open to occupied standby
minimum position

Closed

Failed outdoor air sensor

Open to occupied
minimum position

Open to occupied standby
minimum position

Closed

Outdoor air temperature
present and economizing
possible1

Economizing; damper
controlled between
occupied minimum
position and 100%

Economizing; damper
controlled between
occupied standby
minimum position and
100%

Open and economizing
during unit operation; otherwise closed

Outdoor air temperature
present and economizing
not possible1

Open to occupied minimum position

Open to occupied standby
minimum position

Closed

For an explanation of the economizing feature, see “Economizing (free cooling)” on page 45.

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Modulating outdoor/return air dampers

ASHRAE Cycle 1 conformance
Tracer ZN521 applications with an outside air damper support ASHRAE
Cycle 1 conformance. ASHRAE Cycle 1 operation admits 100% outdoor
air at all times except during a warm-up cycle. A tri-state modulating
damper actuator is required for this operation. For Tracer ZN521
ASHRAE Cycle 1 conformance, configure the minimum position of the
economizer setpoint to 100% open during occupied periods. If the zone
temperature drops 3°F (1.7°C) below the active zone temperature setpoint, the Tracer ZN521 closes the outdoor air damper regardless of the
minimum position setpoint.

ASHRAE Cycle 2 conformance
Tracer ZN521 controller applications with modulating outside air damper
support ASHRAE Cycle 2 conformance. ASHRAE Cycle 2 operation
allows the modulating outdoor air damper to completely close when the
zone temperature drops 3°F (1.7°C) or more below the active zone temperature setpoint. If the zone temperature rises to within 2°F (1.2°C) of the
active setpoint, the damper opens to the occupied or occupied standby
minimum damper positions. If the zone temperature is between 2°F and
3°F (1.2°C and 1.7°C) below the active zone temperature setpoint, the
damper modulates between the minimum position and closed.
If the discharge air temperature is between the discharge air temperature low limit and the discharge air temperature low setpoint, the
damper modulates between the minimum position and closed. If this situation is concurrent with ASHRAE Cycle 2 operation, the lesser of the two
setpoints will determine the actual damper position.

Economizing (free cooling)
Cooling with outdoor air, when the temperature is low enough to make
this possible, is referred to as economizing or free cooling. Tracer ZN521
controller applications with modulating outside air damper support economizing. The modulating outdoor air damper provides the first source of
cooling for the Tracer ZN521. The controller initiates economizing if the
outdoor air temperature is below the economizer enable point (configurable using the Rover service tool). If economizing is initiated, the controller modulates the outdoor air damper (between the active minimum
damper position and 100%) to control the amount of outdoor air cooling
capacity. When the outdoor air temperature rises 5°F (2.8°C) above the
economizer enable point, the controller disables economizing and moves
the outdoor air damper back to its predetermined minimum position
based on the current occupancy mode or communicated minimum outdoor
air damper position. If an outdoor air temperature value is not present,
economizing is disabled.

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Chapter 5 Sequence of operations

Two-position control of a modulating
outdoor air damper
The Tracer ZN521 does not support a two-position outdoor air damper
actuator. However, a modulating outdoor/return air damper actuator can
be used for two-position control. Two-position control can be accomplished
by not providing an outdoor air temperature (neither hard-wired nor communicated) to the controller, and by setting the damper minimum position (using the Rover service tool) to the desired value (typically, 100%).

Face-and-bypass damper operation
The Tracer ZN521 can control a face-and-bypass damper to modulate a
percentage of air to the face of the coil(s) and around (bypass) the coil(s) to
maintain zone comfort. For two-pipe changeover applications, if the controller requests heating and hot water is available, the face-and-bypass
damper modulates to the face position. If the controller requests heating
and hot water is not available, the face-and-bypass damper remains in
the bypass position, and water sampling may be initiated (see “Entering
water temperature sampling function” on page 40). For four-pipe
changeover applications, both heat and cool capacity are assumed to be
available.

Face-and-bypass, isolation-valve operation
A Tracer ZN521 with a face-and-bypass damper controls on/off isolation
valve(s) to prevent unwanted water flow through the coil(s) when no airflow is passing over the coil (100% bypass). In two-pipe applications, the
isolation valve stops water flow, preventing radiant heat (heating mode)
and excessive condensate (cooling mode) from the coil. In four-pipe applications, the isolation valves are used to prevent simultaneous heating
and cooling.
The heating or cooling isolation valve opens whenever capacity is
requested (>0%) as the face-and-bypass damper begins to modulate
toward the coil face. The isolation valve closes when capacity returns to
0%.

DX cooling operation
The Tracer ZN521 supports one stage of direct expansion (DX) compressor operation for cooling only.
Note:
The controller does not use the DX compressor and economizing
simultaneously. Not doing so prevents short cycling from occurring if the entering air temperature is too low for the evaporator coil to operate as designed.

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Electric heat operation

Electric heat operation
The Tracer ZN521 supports both single-stage and two-stage electric heat.
Electric heat is cycled on and off to maintain the discharge air temperature at the active heating setpoint. Two-pipe changeover units with electric heat use the electric heat only when hot water is not available. The
use of both electric and hydronic heat is not supported.

Baseboard heat operation
When configured for baseboard heat output, the controller turns on baseboard heat at 2.2°F (1.2°C) below the active heating setpoint, and turns
off baseboard heat at 0.8°F (0.4°C) below the active heating setpoint. The
range for activating the baseboard heat cannot be adjusted; however, the
heating setpoint is configurable using the Rover service tool.
Baseboard heating is used most effectively when the discharge air temperature control high limit is set below 100°F (56°C). If this is done, the
unit heat will maintain the temperature on light load days and the baseboard heat will be enabled to maintain the temperature on heavier load
days.

Dehumidification
The Tracer ZN521 supports a dehumidification feature. Dehumidification
is possible if the following are present:

•
•
•
•
•

Mechanical cooling is available
The heating capacity is located in the reheat position
A zone humidity sensor is connected at AI4, or a relative humidity
(RH) value is transmitted to the controller by a BAS.
The Space RH Setpoint is valid (configurable using the Rover service
tool)
Dehumidification is enabled using the Rover service tool

The controller initiates dehumidification if the zone humidity exceeds the
humidity setpoint. The controller continues to dehumidify until the
sensed humidity falls below the setpoint minus the relative humidity offset.
The controller uses cooling and heating capacities simultaneously to
dehumidify the space. While dehumidifying, the controller maintains the
zone temperature at the active setpoint.
Note:
Dehumidification is not available for face-and-bypass applications, and cannot be used if the unit is in the unoccupied mode.
Dehumidification disables the economizing function.

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Chapter 5 Sequence of operations

Peer-to-peer communication
Tracer ZN521 zone controllers have the ability to share data with other
LonTalk-based controllers. Multiple controllers can be bound as peers,
using the Rover service tool, to share:

•
•
•
•
•

Setpoint
Zone temperature
Heating/cooling mode
Fan status
Unit capacity control

Shared data is communicated from one controller to any other controller
that is bound to it as a peer. Applications having more than one unit serving a single zone can benefit by using this feature; it allows multiple units
to share a single zone temperature sensor and prevents multiple units
from simultaneously heating and cooling.

Unit protection strategies
The following strategies are initiated when specific conditions exist in
order to protect the unit or building from damage:

•
•
•
•
•
•
•
•

Smart reset
Low-coil-temperature protection
Condensate overflow
Fan status
Fan off delay
Filter-maintenance timer
Freeze avoidance
Freeze protection (discharge air temperature low limit)

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Unit protection strategies

Smart reset
The Tracer ZN521 will automatically restart a unit that is locked-out as a
result of a Low Coil Temp Detection (BI1) diagnostic. Referred to as
“smart reset,” this automatic restart will occur 30 minutes after the diagnostic occurs. If the unit is successfully restarted, the diagnostic is
cleared. If the unit undergoes another Low Coil Temp Detection diagnostic within a 24-hour period, the unit will be locked out until it is manually
reset. (For more information on manual resetting, see “Manual (latching)
diagnostics” on page 58).

Low-coil-temperature protection
See “BI1: Low-coil-temperature detection” on page 14 and “Smart reset”
above.

Condensate overflow
See “BI2: Condensate overflow” on page 14.

Fan status
The fan status is based on the status of the binary output(s) dedicated to
fan control. The fan status is reported as high, medium, or low whenever
the corresponding binary output is energized. The fan status is reported
as off whenever none of the fan binary outputs are energized.
Additionally, a fan-status switch can be connected to BI4 to monitor the
status of the fan for belt-driven or direct-driven units. The fan status
switch provides feedback to the controller. If the fan is not operating when
the controller has the fan controlled to on, the controller will generate a
Low AirFlow—Fan Failure diagnostic.
If the controller energizes the fan output for 1 minute, and the fan status
switch indicates no fan operation, the controller performs a unit shutdown and generates a Low AirFlow—Fan Failure diagnostic. If the fan
has been operating normally for one minute, but the fan status switch
indicates no fan operation, the same diagnostic is generated. This manual
diagnostic discontinues unit operation until the diagnostic has been
cleared from the controller. If a diagnostic reset is sent to the controller
and the fan condition still exists, the controller attempts to run the fan for
1 minutes before generating another diagnostic and performing a unit
shutdown.

Fan off delay
After heating has been controlled off, the Tracer ZN521 keeps the fan
energized for an additional 30 seconds. The purpose of this feature is to
remove residual heat from the heating source.

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Chapter 5 Sequence of operations

Filter-maintenance timer
The filter-maintenance timer tracks the amount of time (in hours) that
the fan is enabled. The Maintenance Required Timer Setpoint (configurable using the Rover service tool) is used to set the amount of time until
maintenance (typically, a filter change) is needed. If the setpoint is configured to zero, the filter-maintenance timer is disabled.
The controller compares the fan-run time to Maintenance Required Timer
Setpoint. Once the setpoint is reached, the controller generates a Maintenance Required diagnostic. When the diagnostic is cleared, the controller
resets the filter-maintenance timer to zero, and the timer begins accumulating fan-run time again.

Freeze avoidance
Freeze avoidance is used for low ambient temperature protection. It is initiated only when the fan is off. The controller enters the freeze-avoidance
mode when the outdoor air temperature is below the Freeze Avoidance
Setpoint (configurable using the Rover service tool). The controller disables freeze avoidance when the outdoor air temperature rises 3°F (1.7°C)
above the Freeze Avoidance Setpoint.
When the controller is in freeze-avoidance mode:

•
•
•
•
•
•
•

Valves are driven open to allow water to flow through the coil
Fan is off
Face-and-bypass damper (when present) is at full bypass
Economizing is disabled
The outdoor/return air damper is closed
DX cooling is off
Electric heat stages are off

Freeze protection (discharge air temperature low limit)
The controller monitors the discharge air temperature with a 10 kΩ thermistor wired to analog input AI2. The freeze-protection operation is initiated whenever the discharge air temperature falls below the Discharge
Air Temperature Low Limit. The Discharge Air Temperature Low Limit
is configurable using the Rover service tool. During freeze protection, the
controller increases the heating capacity or decreases the cooling capacity
in order to raise the discharge air temperature above the low limit. If the
discharge air temperature remains below the low limit for 3 minutes, the
controller generates a Discharge Air Temp Limit diagnostic. See Table 16
on page 59 for the effects of this diagnostic on outputs.

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Chapter 6

Status indicators for
operation and
communication
This chapter describes the operation and communication status indicators on the Tracer ZN521 controller, including:

•

A description of the location and function of the Test button and Service pin button and the light-emitting diodes (LEDs) located on the
controller
A complete list of the diagnostics that can occur, their effect on controller outputs, and an explanation of how diagnostics are cleared and
the device restored to normal operation

Test button
The Test button is used to perform the manual output test (see “Manual
output test” on page 52), which verifies that the controller output devices
are operating properly. It is located on the Tracer ZN521 circuit board as
shown in Figure 19. You must remove the cover to access the Test button.
Figure 19. Tracer ZN521 zone controller circuit board
Green (status)
LED

Test button

Neuron ID label

Red (service) LED
Service pin button
Yellow
(communication)
LED

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Chapter 6 Status indicators for operation and communication

Manual output test
The manual output test sequentially turns on and off all binary outputs
to verify their operation. The test overrides normal operation of the controller, which is suspended while the test is being performed.
Use the manual output test to:

•
•
•

Verify output wiring and operation
Force the water valve(s) open to balance the hydronic system
Clear diagnostics and restore normal operation (although not a primary function of the manual output test)

The manual output test is performed either by repeatedly pressing the
Test button to proceed through the test sequence or by using the Rover
service tool. Table 11 on page 53 lists the outputs for non-face-and-bypass
unit configurations in the sequence in which they are verified; Table 12
on page 55 lists the outputs for face-and-bypass unit configurations in the
sequence in which they are verified.
The procedure is as follows:
1. Press and hold the Test button for 3 to 4 seconds, then release it to
start the test mode. The green (status) LED goes off when you press
the Test button, and then it blinks (as described in Table 14 on
page 57) when the Test button is released to indicate that the controller is in manual test mode.
2. Press the Test button (no more than once per second) to advance
through the test sequence. Table 11 and Table 12 show the resulting
activities of the binary outputs.
Note:
The outputs are not subject to minimum on or off times during
the test sequence.

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Begins test
mode1

Fan high2

Fan
medium3

Fan low4

Main open,
DX on

Main close,
DX off, aux
open, EH1
on

Aux open,
EH1 on,
exhaust
fan5

Aux close,
EH1 off,
EH2 on,
damper
open

Damper
close

Generic/
baseboard
heat
energized6

Result

Number of times
Test button is pressed

Step

On/High

Off

1) Off
2) On

Off

1) On/Med
2) Off

Off

On/High

Off

On/Low

Off

On/Open

Off

On/Close

Off

On/Open

Off

On/Close

Off

1) On/Close
2) Off

Fan high

Off

BOP2

1)Fan medium
2)Exhaust

On/Close

BOP3

Fan low

Off

BOP4
1)Cooling/changeover
valve, open
2)Two-position cooling/
changeover valve
3)DX compressor

Off

BOP5

Cooling/changeover
valve, close

Off

BOP6
1)Heating valve, open
2)Two-position heat valve
3)Electric heat, stage 1

Off

BOP7

1)Heating valve, close
2)Electric heat, stage 2

BOP1

Off

On/Open

Off

On/Close

Off

On/Close

Outdoor air damper, open
Off

BOP9
Outdoor air damper, close

BOP8

BOP10

Off

1)Generic
2)Baseboard heat

Table 11. Manual output test sequence for non-face-and-bypass configurations

Manual output test

Result

BOP7

1)Heating valve, close
2)Electric heat, stage 2

BOP6
1)Heating valve, open
2)Two-position heat valve
3)Electric heat, stage 1

BOP5

Cooling/changeover
valve, close

BOP4
1)Cooling/changeover
valve, open
2)Two-position cooling/
changeover valve
3)DX compressor

BOP3

Fan low

BOP2

1)Fan medium
2)Exhaust

BOP1

BOP9

BOP8
Outdoor air damper, open

Fan high

BOP10

The controller turns off all fan and electric heat outputs and drives all dampers and valves closed.
The controller attempts to clear all diagnostics.
If configured for a 3-speed fan, the medium fan speed output will energize at step 3. If configured for a 2-speed fan, the fan remains on high speed at
step 3.
If configured for a 3-speed fan, the medium fan speed output energizes at step 4. If configured for a 2-speed fan, the low fan speed output energizes at
step 4. If configured for a 1-speed fan, the fan remains on high speed at step 4.
If the unit is configured for a 1- or 2-speed fan, the exhaust fan output energizes on step 7. The exhaust fan output is shared with medium fan speed.
After step 10, the manual output test performs an exit, which initiates a reset to restore the controller to normal operation.

11: Exit5

Number of times
Test button is pressed

Step
Outdoor air damper, close

54
1)Generic
2)Baseboard heat

Table 11. Manual output test sequence for non-face-and-bypass configurations
Chapter 6 Status indicators for operation and communication

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Manual output test

BOP5

BOP6

BOP7

Two-position heat valve

Face and bypass damper,
close (bypass)

BOP8

BOP9
Outdoor air damper, close

BOP4

Outdoor air damper, open

BOP3

Begins test
mode1

Off

On/Close

Off

On/Close

Off

Fan high2

On/High

Off

On/Open

Off

Fan
medium3

Off

1) On/Med
2) Off

Off

On/Open

Off

Fan low4

Off

On/Low

Off

On/Open

Off

Main open,
DX on

On/High

Off

On/Open

Off

Main close,
DX off, aux
open

On/High

Off

On/Open

Off

Aux open,
EH1 on,
exhaust
fan5

On/High

1) Off
2) On

Off

On/Open

Off

Aux close,
damper
open

On/High

Off

On/Close

On/Open

Off

Outdoor air
damper
close

On/High

Off

On/Close

Off

On/Close

Off

Generic/
baseboard
heat
energized6

On/High

Off

On/Close

Off

1)Generic

Number of times
Test button is pressed

Face and bypass damper,
open to face

BOP2

Two-position cool/
changeover valve

BOP1

Fan low

Result

1)Fan medium
2)Exhaust fan

Step

Fan high

Table 12. Manual output test sequence for face-and-bypass configurations (two-position isolation valves
only)

11: Exit5
1
2
3

5
6

The controller turns off all fan and electric heat outputs and drives all dampers and valves closed.
The controller attempts to clear all diagnostics.
If configured for a 3-speed fan, the medium fan speed output will energize at step 3. If configured for a 2-speed fan, the fan remains on high
at step 3.
If configured for a 3-speed fan, the medium fan speed output energizes at step 4. If configured for a 2-speed fan, the low fan speed output en
at step 4. If configured for a 1-speed fan, the fan remains on high speed at step 4.
If the unit is configured for a 1- or 2-speed fan, the exhaust fan output energizes on step 7. The exhaust fan output is shared with medium fan
After step 10, the manual output test performs an exit, which initiates a reset to restore the controller to normal operation.

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Chapter 6 Status indicators for operation and communication

Service pin button
The Service pin button is located as shown in Figure 19 on page 51. The
Service pin button is used to:

•
•
•
•

Identify a device (see “Identifying a device” in the Rover Installation/
Operation/Programming guide (EMTX-SVX01A-EN)
Add a device to the active group (see “Adding a device” in EMTXSVX01A-EN)
Verify PCMCIA communications (see “Verifying PCMCIA communications” in EMTX-SVX01A-EN)
Make the green (status) LED “wink” to verify that the controller is
communicating on the link (see Table 14 on page 57 and “Setting the
Auto-wink option” in EMTX-SVX01A-EN)

Interpreting LEDs
The red (service) LED on the Tracer ZN521 controller (see Figure 19 on
page 51) indicates whether the controller is capable of operating normally
(see Table 13).
Table 13. Red LED: Service indicator
LED activity

Explanation

LED is off continuously when power
is applied to the controller.

The controller is operating normally.

LED is on continuously when power
is applied to the controller.

The controller is not working properly, or someone is pressing the Service pin button.

LED flashes once every second.

The controller is not executing the
application software because the network connections and addressing
have been removed.1

Restore the controller to normal operation using the Rover service tool. Refer to
EMTX-SVX01A-EN for more information.

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Interpreting LEDs

The green (status) LED on the Tracer ZN521 controller (see Figure 19 on
page 51) indicates whether the controller has power applied to it and if
the controller is in manual test mode (see Table 14).
Table 14. Green LED: Status indicator
LED activity

Explanation

LED is on continuously.

Power is on (normal operation).

LED blinks (one recurring blink).

Manual output test mode is being
performed and no diagnostics are
present.

LED blinks (blinks twice as a recurring sequence).

Manual output test mode is being
performed and one or more diagnostics are present.

LED blinks (1/4 second on,
1/4 second off for 10 seconds).

The Auto-wink option is activated,
and the controller is
communicating.1

LED is off continuously.

Either the power is off,
the controller has malfunctioned, or
the Test button is being pressed.

By sending a request from the Rover service tool, you can request the controller’s
green LED to blink (“wink”), a notification that the controller received the signal
and is communicating.

The yellow (communications) LED on the Tracer ZN521 controller (see
Figure 19 on page 51) indicate the controller’s communication status (see
Table 15).
Table 15. Yellow LED: Communications indicator
LED activity

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Explanation

LED is off continuously

The controller is not detecting any
communication (normal for standalone applications).

LED blinks.

The controller detects communication (normal for communicating
applications, including data sharing).

LED is on continuously.

Problem with communication link
wiring (possible need for termination
resistor), or controller failure (caused
by power surge, lightning strike, etc.)

Chapter 6 Status indicators for operation and communication

Diagnostics
Diagnostics are informational messages that indicate the operational status of the controller. In response to most diagnostics, the controller
attempts to protect the equipment by enabling or disabling, or opening or
closing, specific outputs. Other diagnostics provide information about the
status of the controller, but have no effect on outputs. Diagnostics are
reported in the order in which they occur. Multiple diagnostics can be
present simultaneously. Diagnostic messages are viewed using the Rover
service tool or through a BAS.

Types of diagnostics
Diagnostics are categorized according to the type of clearing method each
uses and the type of information each provides.
The four categories are:

•
•
•
•

Manual (latching)
Automatic (nonlatching)
Smart reset
Informational
Note:
Clearing diagnostics refers to deleting diagnostics from the
software; it does not affect the problem that generated the message. For help with diagnosing a problem, see Chapter 7, “Troubleshooting”.

Manual (latching) diagnostics
Manual diagnostics (also referred to as latching) cause the unit to shut
down. Manual diagnostics can be cleared from the controller in one of the
following ways:

•

•
•
•
•

By using the Rover service tool (see “Resetting a diagnostic” in
EMTX-SVX01A-EN, Rover Installation/Operation/and Programming guide).
Through a building automation system (see product literature)
By initiating a manual output test at the controller (see “Manual output test” on page 52)
By cycling power to the controller. When the 24 Vac power to the controller is cycled off and then on again, a power-up sequence occurs.
By turning the zone sensor fan switch to OFF and then back to any
other setting. (This feature will be available beginning with controller
software version 2.10.)

Automatic (nonlatching) diagnostics
Automatic diagnostics clear automatically when the problem that generated the diagnostic is solved.

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Diagnostics

Smart reset diagnostics
After the controller detects the first smart reset diagnostic, the unit waits
30 minutes before initiating the smart reset function. If another diagnostic of this type occurs again within 24 hours after an automatic clearing,
you must clear the diagnostic manually by using any of the ways shown
for “Manual (latching) diagnostics.”

Informational diagnostics
Informational diagnostics provide information about the status of the
controller. They do not affect machine operation. They can be cleared from
the controller using any of the ways shown for “Manual (latching) diagnostics.”

Table of diagnostics
Table 16 The tables present each diagnostic that can be generated by the
Tracer ZN521, its effect on outputs (consequences), and its type.
Note:
The generic binary output is unaffected by diagnostics.
Table 16. Diagnostics
Diagnostic

Diagnostic
type

Probable cause

Consequences

Maintenance Required

Fan run hours exceed the
time set to indicate filter
change

Fan unaffected
Valves unaffected
Electric heat unaffected
Face and bypass damper unaffected

Informational

Condensate Overflow

The drain pan is full of
water

Fan off
Valves closed
Outdoor air damper closed
Face and bypass damper bypass
DX/electric heat off
Baseboard heat off

Manual

Low Coil Temp Detection

The leaving fluid temperature may be close to
freezing

Fan off
Valves open
Outdoor air damper closed
Face and bypass damper bypass
DX/electric heat off
Baseboard heat off

Smart reset/
Manual

Low Airflow—Fan Failure

The fan drive belt, contactor, or motor has
failed.

Fan off
Valves closed
Outdoor air damper closed
Face and bypass damper bypass
DX/electric heat off
Baseboard heat off

Manual

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Chapter 6 Status indicators for operation and communication

Table 16. Diagnostics (Continued)
Diagnostic

Probable cause

Consequences

Diagnostic
type

Space Temperature Failure

Invalid or missing value
for zone temperature

Fan off
Valves closed
Outdoor air damper closed
Face and bypass damper bypass
DX/electric heat off
Baseboard heat off

Automatic

Entering Water Temp Failure

Invalid or missing value
for zone temperature

Fan unaffected (enabled)
Valves unaffected
Outdoor air damper unaffected
Face and bypass damper unaffected
DX/electric heat unaffected
Baseboard heat off

Automatic

Discharge Air Temp Limit

Discharge air temperature has fallen below the
Discharge Air Temperature Low Limit

Fan off
Valves open
Outdoor air damper closed
Face and bypass damper bypass
DX/electric heat off
Baseboard heat off

Automatic

Discharge Air Temp Failure

Invalid or missing value
for discharge air temperature

Fan off
Valves closed
Outdoor air damper closed
Face and bypass damper bypass
DX cooling/electric heat off
Baseboard heat off

Automatic

Outdoor Air Temp Failure

Invalid or missing value
for outdoor air temperature

Fan unaffected
Valved unaffected
Outdoor air damper minimum
position
Face and bypass damper unaffected
DX cooling/electric heat unaffected
Baseboard heat unaffected

Automatic

Humidity Input Failure

Invalid or missing value
for relative humidity

Fan unaffected
Valves unaffected
Outdoor air damper unaffected
Face and bypass damper unaffected
DX cooling/electric heat unaffected
Baseboard heat unaffected
Dehumidification sequence off

Automatic

CO2 Sensor Failure

Invalid or missing value
for CO2

Fan unaffected
Valves unaffected
Outdoor air damper unaffected
Face and bypass damper unaffected
DX cooling/electric heat unaffected
Baseboard heat unaffected

Informational

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Diagnostics

Table 16. Diagnostics (Continued)
Probable cause

Consequences

Diagnostic
type

Generic AIP Failure

Invalid or missing value
for generic analog input

Fan unaffected
Valves unaffected
Outdoor air damper unaffected
Face and bypass damper unaffected
DX cooling/electric heat unaffected
Baseboard heat unaffected

Informational

Local Fan Mode Failure

Invalid or missing fanspeed switch (reverts to
default fan speed)

Fan unaffected
Valves unaffected
Outdoor air damper unaffected
Face and bypass damper unaffected
DX cooling/electric heat unaffected
Baseboard heat unaffected

Automatic

Local Setpoint Failure

Invalid or missing value
for zone temperature setpoint (reverts to default
setpoint)

Fan unaffected
Valves unaffected
Outdoor air damper unaffected
Face and bypass damper unaffected
DX cooling/electric heat unaffected
Baseboard heat unaffected

Automatic

Generic Temperature Failure

Invalid or missing
generic temperature
value

Fan unaffected
Valves unaffected
Outdoor air damper unaffected
Face and bypass damper unaffected
DX cooling/electric heat unaffected
Baseboard heat unaffected

Informational

Invalid Unit Configuration

Software is configured
improperly

Fan off
Valves off
Outdoor air damper closed
Face and bypass damper closed
DX cooling/electric heat off
Baseboard heat off

Manual

Normal

On start-up

Fan unaffected
Valves unaffected
Electric heat unaffected
Compressors unaffected
Damper unaffected

Automatic

Diagnostic

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Chapter 6 Status indicators for operation and communication

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Chapter 7

Troubleshooting
Use Table 17 through Table 22 to assist you in diagnosing any of the following operational problems that you might encounter with the Tracer
ZN521 zone controller:

•
•
•
•
•
•
•

Fan does not energize (Table 17)
Valves remain closed (Table 18 on page 64)
Valves remain open (Table 19 on page 65)
Compressors are not running (Table 20 on page 65)
Electric heat does not energize (Table 20 on page 65)
An outdoor air damper stays closed (Table 21 on page 66)
An outdoor air damper stays open (Table 22 on page 66)

Table 17. Fan does not energize
Probable cause

Explanation

Unit wiring

The wiring between the controller outputs and the fan relays and contacts must be
present and correct for normal fan operation. Refer to applicable wiring diagram.

Failed end device

The fan motor and relay must be checked to ensure proper operation.

Normal operation

The fan will turn off when the controller receives a communicated off signal, when the
fan-speed switch is set to OFF, when specific diagnostics are generated, or when the
default fan speed is set to Off and the fan is operating in the Auto mode. If the controller
is in unoccupied mode, the fan cycles between off and the highest fan speed.

No power to the controller

If the controller does not have power, the unit fan does not operate. For the Tracer ZN521
controller to operate normally, it must have an input voltage of 24 Vac. If the green LED is
off continuously, the controller does not have sufficient power or has failed.

Power-up control-wait

If power-up control-wait is enabled (non-zero time), the controller remains off until one of
two conditions occurs:
1) The controller exits power-up control-wait after it receives communicated information.
2) The controller exits power-up control-wait after the power-up control-wait time expires.

Diagnostic present

Several diagnostics affect fan operation. For information about these diagnostics, see
Table 16 on page 59.

Unit configuration

The controller must be properly configured based on the actual installed end devices and
application. If the unit configuration does not match the actual end device, the fans may
not work correctly.

Manual output test

The controller includes a manual output test sequence you can use to verify output operation and associated output wiring. However, based on the current step in the test
sequence, the unit fan may not be on. Refer to the “Manual output test” on page 52.

Random start
observed

After power-up, the controller always observes a random start from 5 to 30 seconds. The
controller remains off until the random start time expires.

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Chapter 7 Troubleshooting

Table 17. Fan does not energize (Continued)
Probable cause

Explanation

Cycling fan operation/
continuous

The controller operates the fan continuously when in the occupied, occupied standby, or
occupied bypass mode. When the controller is in the unoccupied mode, the fan is cycled
between high speed and off with capacity.

Unoccupied operation

Even if the controller is configured for continuous fan operation, the fan normally cycles
with capacity during unoccupied mode. While unoccupied, the fan cycles on or off with
heating/cooling to provide varying amounts of heating or cooling to the space.

Fan mode off

If a local fan mode switch determines the fan operation, the off position controls the fan
off.

Requested mode off

You can communicate a desired operating mode (such as off, heat, and cool) to the controller. If off is communicated to the controller, the unit controls the fan off. There is no
heating or cooling.

Table 18. Valves remain closed
Probable cause

Explanation

Unit wiring

The wiring between the controller outputs and the valve(s) must be present and correct
for normal valve operation. Refer to applicable wiring diagram.

Failed end device

The valves must be checked to ensure proper operation.

No power to the controller

If the controller does not have power, the unit valve(s) will not operate. For the Tracer
ZN521 controller to operate normally, you must apply an input voltage of 24 Vac. If the
green LED is off continuously, the controller does not have sufficient power or has failed.

Power-up control-wait

Diagnostic present

Several diagnostics affect valve operation. For information about these diagnostics, see
Table 16 on page 59.

Normal operation

The controller opens and closes the valves to meet the unit capacity requirements.

Unit configuration

The controller must be properly configured based on the actual installed end devices and
application. If the unit configuration does not match the actual end device, the valves
may not work correctly.

Manual output test

The controller includes a manual output test sequence you can use to verify output operation and associated output wiring. However, based on the current step in the test
sequence, the valves may not be open. Refer to the “Manual output test” on page 52.

Random start
observed

After power-up, the controller always observes a random start from 5 to 30 seconds. The
controller remains off until the random start time expires.

Requested mode off

You can communicate a desired operating mode (such as off, heat, and cool) to the controller. If off is communicated to the controller, the unit controls the fan off. There is no
heating or cooling.

Entering water
temperature
sampling logic

The controller includes entering water temperature sampling logic, which is automatically initiated during 2-pipe and 4-pipe changeover if the entering water temperature is
either too cool or too hot for the desired heating or cooling. (See “AI1: Entering water
temperature” on page 17.)

Valve configuration

Make sure the valves are correctly configured, using the Rover service tool, as normally
open or normally closed as dictated by the application.

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Troubleshooting

Table 19. Valves remain open
Probable cause

Explanation

Unit wiring

The wiring between the controller outputs and the valve(s) must be present and correct
for normal valve operation. Refer to applicable wiring diagram.

Failed end device

The valves must be checked to ensure proper operations.

Normal operation

The controller opens and closes the valves to meet the unit capacity requirements.

Manual output test

The controller includes a manual output test sequence you can use to verify output operation and associated output wiring. However, based on the current step in the test
sequence, the values may not be open. refer to the “Manual output test” on page 52.

Diagnostic present

Several diagnostics affect valve operation. For information about these diagnostics, see
Table 16 on page 59.

Unit configuration

Entering water
temperature
sampling logic

The controller includes entering water temperature sampling logic, which is automatically
initiated during 2-pipe and 4-pipe changeover if the entering water temperature is either
too cool or too hot for the desired heating or cooling. (See “AI1: Entering water temperature” on page 17.)

Valve configuration

Make sure the valves are correctly configured, using the Rover service tool, as normally
open or normally closed as dictated by the application.

Freeze avoidance

When the fan is off with no demand for capacity (0%) and the outdoor air temperature is
below the freeze avoidance setpoint, the controller opens the water valves (100%) to prevent coil freezing. This includes unoccupied mode when there is no call for capacity or
any other time the fan is off.

Table 20. DX or electric heat does not energize
Probable cause

Explanation

Unit wiring

The wiring between the controller outputs and the end devices must be present and correct for normal operation. Refer to applicable wiring diagram.

Failed end device

Check the control contactors or the electric heat element, including any auxiliary safety
interlocks, to ensure proper operation.

No power to the
controller

If the controller does not have power, heat outputs do not operate. For the Tracer ZN521
controller to operate normally, you must apply an input voltage of 24 Vac. If the green
LED is off continuously, the controller does not have sufficient power or has failed.

Diagnostic present

Several diagnostics affect DX and electric heat operation. For information about these
diagnostics, see Table 16 on page 59.

Normal operation

The controller controls compressor or electric heat outputs as needed to meet the unit
capacity requirements.

Unit
configuration

The controller must be properly configured based on the actual installed end devices and
application. If the unit configuration does not match the actual end device, DX or electric
heat may not operate correctly.

Manual output test

The controller includes a manual output test sequence you can use to verify output operation and associated output wiring. However, based on the current step in the test
sequence, the DX or electric heat outputs may be off. Refer to the “Manual output test”
on page 52.

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Chapter 7 Troubleshooting

Table 20. DX or electric heat does not energize (Continued)
Probable cause

Explanation

Requested mode off

You can communicate a desired operating mode (such as off, heat, and cool) to the controller. If off is communicated to the controller, the unit shuts off the compressor or electric heat.

Freeze avoidance

When the fan is off with no demand for capacity (0%) and the outdoor air temperature is
below the freeze avoidance setpoint, the controller disables compressors and electric
heat outputs (100%) to prevent coil freezing. This includes unoccupied mode when there
is no call for capacity or any other time the fan is off.

Table 21. Outdoor air damper remains closed
Probable cause

Explanation

Unit wiring

The wiring between the controller outputs and the outdoor air damper must be present
and correct for normal outdoor air damper operation. Refer to applicable wiring diagram.

Failed end device

Check damper actuator to ensure proper operation.

No power to the
controller

If the controller does not have power, the outdoor air damper does not operate. For the
Tracer ZN521 controller to operate normally, you must apply an input voltage of 24 Vac. If
the green LED is off continuously, the controller does not have sufficient power or has
failed.

Diagnostic present

Several diagnostics affect outdoor air damper operation. For information about these
diagnostics, see Table 16 on page 59.

Normal
operation

The controller opens and closes the outdoor air damper based on the controller’s occupancy mode and fan status. Normally, the outdoor air damper is open during occupied
mode when the fan is running and closed during unoccupied mode.

Unit configuration

The controller must be properly configured based on the actual installed end devices and
application. If the unit configuration does not match the actual end device, the outdoor air
damper may not work correctly.

Manual output test

The controller includes a manual output test sequence you can use to verify output operation and associated output wiring. However, based on the current step in the test
sequence, the outdoor air damper may not be open. Refer to the “Manual output test” on
page 52.

Warm-up and cooldown sequence

The controller includes both a morning warm-up and cool-down sequence to keep the
outdoor air damper closed during the transition from unoccupied to occupied. This is an
attempt to bring the space under control as quickly as possible.

Requested mode off

You can communicate a desired operating mode (such as off, heat, or cool) to the controller. If off is communicated to the controller, the unit closes the outdoor air damper.

Table 22. Outdoor air damper remains open
Probable cause

Explanation

Unit wiring

The wiring between the controller outputs and the outdoor air damper must be present
and correct for normal outdoor air damper operation. Refer to applicable wiring diagram.

Failed end device

Check damper actuator to ensure proper operation.

CNT-SVX07C-EN

Troubleshooting

Table 22. Outdoor air damper remains open (Continued)
Probable cause

Explanation

Normal
operation

Unit
configuration

Manual output test

The controller includes a manual output test sequence you can use to verify output operation and associated output wiring. However, based on the current step in the test
sequence, the outdoor air damper may be open. Refer to the “Manual output test” on
page 52.

CNT-SVX07C-EN

Chapter 7 Troubleshooting

CNT-SVX07C-EN

Index
Numerics

24 Vac wiring, 7

BAS communication, 1, 9

Baseboard heat
Operation, 47
Supported application, 21

AC-power wiring, 7
Actuators
Damper, 5, 46
Valve, 4
Additional application-dependent
components, 4–5
Addressing
LonTalk communication, 9
Neuron IDs, 9
Agency listing/compliance, 3
Analog inputs, 16–20
AI1 (Entering water temperature),
17
AI2 (Discharge air temperature), 18
AI3 (Outdoor air temperature), 18
AI3 configuration options, 18
AI4 (Universal 4–20 mA), 19
AI4 configuration options, 19
AI4 configured for CO2
measurement, 20
AI4 configured for RH
measurement, 20
AI4 generic configuration, 19
FAN (Fan mode input), 17
Generic temperature, 18
SET (Local setpoint), 17
ZN (Zone temperature), 16
Applications, 1, 13–34
Applications table, 13
ASHRAE Cycle 1
Agency listing/compliance, 4
Operation, 45
ASHRAE Cycle 2
Agency listing/compliance, 4
Operation, 45

CNT-SVX07C-EN

Binary inputs, 14–15
BI1 (Low-coil-temperature
detection), 14
BI2 (Condensate overflow), 14
BI3 (Occupancy or generic), 15
BI3 configuration options, 15
BI4 (Fan status), 15
Switching devices, 4
Binary outputs, 21–22
Generic, 21
Manual output test, 52
Output devices, 4
Overriding, 22
Table of supported options, 21
Blower coils, 1, 21
Building automation system
communication, 1, 9

C
CE, see Agency listing/compliance
Circuit board, 51
Clearances, 2
Clearing diagnostics, 58
CO2
Measurement input, 20
Sensor, 5, 20
Sensor failure diagnostic, 60
Condensate overflow
Diagnostic, 59
Input, 14
Switch, 4, 14
Configuration options
AI3 (Outdoor air temperature or
generic), 18
AI4 (Generic, CO2 measurement, or
RH measurement), 19
BI3 (Occupancy or generic), 15
DX cooling, 1

Index

Electric heat, 1
Face-and-bypass dampers, 1
Outdoor/return air dampers, 1
Rover service tool, 1
Tri-state modulating dampers, 1
Tri-state modulating valves, 1
Two-position valves, 1
Current-sensing switches, 4

D
Dampers
Actuators, 5
Exhaust, 41
Face-and-bypass, 1, 21, 46
Modulating outdoor/return air,
43, 46
Outdoor/return air, 1, 21, 41, 43
Supported applications, 1, 21
Tri-state modulating, 1
Two-position control, 46
Data sharing, 48
Dehumidification, 47
Device addressing for BAS
communication, 9
Diagnosing operational problems,
63–67
Diagnostics
Automatic, 58
Clearing, 58
CO2 Sensor Failure, 60
Condensate Overflow, 59
Discharge Air Temp Failure, 60
Discharge Air Temp Limit, 60
Entering Water Temp Failure, 60
Freeze protection, 60
Generic AIP Failure, 61
Generic Temperature Failure, 61
Humidity Input Failure, 60
Informational, 59
Invalid Unit Configuration, 61
Latching, 58
Local Fan Mode Failure, 61
Local Setpoint Failure, 61
Low Coil Temp Detection, 59
Maintenance (filter change), 59
Manual, 58
Nonlatching, 58
Normal, 61
Outdoor Air Temp Failure, 60
Smart reset, 59
Table, 59
Types, 58

Zone Temp Failure, 59
Dimensional diagram, 3
Dimensions, 2
Discharge air temperature
Failure diagnostic, 60
Low limit diagnostic, 60

G
Generic
Binary input, 15
Binary output, 59
Temperature input, 18
Generic AIP failure diagnostic, 61

Discharge air temperature input, 18

Generic binary input, 15

Discharge air temperature low limit,
50

Generic binary output, 21

Discharge air tempering, 39
DX cooling
Operation, 46
Supported application, 21
Troubleshooting, 65

E
Economizing, 19, 45
Electric heat
Operation, 47
Supported application, 21
Troubleshooting, 65
Entering water temperature
Diagnostic, 60
Input, 17
Sampling function, 40
Equipment supported, 1, 13, 21
Exhaust control, 41

Generic temperature failure
diagnostic, 61

H
Heating or cooling mode, 39
Humidity
Input failure diagnostic, 60
Measurement input, 20
Zone sensor, 20
Hydronic cooling, 21

I
Informational diagnostics, 59
Input/output functions, 13–34
Input/output terminal wiring, 7
Invalid unit configuration
diagnostic, 61
Isolation valve operation, 46

F
Fan
Exhaust, 41
Mode input, 17
Operation, 40
Supply, 41
Troubleshooting, 63
Fan coils, 1, 21
Fan off delay, 49

L
LEDs
General, 51
Interpreting green (status), 57
Interpreting red (service), 56
Interpreting yellow
(communications), 57
Location, 51

Fan status
Input, 15
Switching devices, 4
Unit protection, 49

Local fan mode input failure
diagnostic, 61

Filter-maintenance timer, 50

LonTalk communication
Description, 1
Termination resistors, 9
Wiring and addressing, 9

Four-pipe operation, 43
Free cooling, see Economizing
Freeze avoidance, 19, 50
Freeze protection, 50

Local setpoint failure diagnostic, 61
Local setpoint input, 17

LonTalk protocol, see LonTalk
communication

Freeze-protection switch, 4, 14

CNT-SVX07C-EN

Index

Low-coil-temperature detection
Diagnostic, 14, 59
Input, 14

Overriding binary outputs, 22
General, 52

P
Peer-to-peer communication, 48

Manual output test, 52

Power transformers, 4, 7

Modulating outdoor/return air
dampers, 43

Power wiring, 7

Modulating valves
Calibration, 42
Operation, 42
Morning cool-down, 39

Power-up sequence, 35
Product description, 1
Protection strategies, see Unit
protection strategies

Morning warm-up, 39
Mounting
Cover, 12
Diagram, 12
Location, 11
Operating environment, 11
Procedures, 12

N
National Electrical Code, 7, 8, 9
Neuron IDs
Description, 9
Location of label, 51

R
Random start, 35
Rover service tool
Adding a device, 56
Configuring the controller, 1
Identifying a device, 56
User guide, 1
Verifying LonTalk
communication, 56
Verifying PCMCIA
communications, 56

S
O

Sensor
Humidity, 47

Occupancy
Switch, 15
Switching devices, 4

Sensors
Application-specific, 19
CO2, 5, 20
Table of options, 5
Water and duct temperature, 4
Zone humidity, 5, 20
Zone temperature, 4

Occupancy input, 15
Occupancy modes, 36
General, 36
Occupied, 36
Occupied bypass, 37
Occupied standby, 36
Unoccupied, 36
Operating environment, 11
Outdoor air damper
Troubleshooting, 66
Outdoor air temperature
Failure diagnostic, 60
Input, 18
Outdoor air temperature input, 18
Outdoor/return air dampers, 43
Output devices, 4

CNT-SVX07C-EN

Sequence of operations, 35–50
ASHRAE Cycle 1, 45
ASHRAE Cycle 2, 45
Baseboard heat, 47
Dehumidification, 47
Discharge air temperature low
limit, 50
DX cooling, 46
Economizing, 45
Electric heat, 47
Exhaust control, 41
Face-and-bypass damper, 46
Fan off delay, 49
Fan operation, 40

Fan status, 49
Filter-maintenance timer, 50
Four-pipe operation, 43
Freeze avoidance, 50
Freeze protection, 50
Heating/cooling mode, 39
Isolation valve, 46
Modulating-valve calibration, 42
Modulating-valve operation, 42
Morning cool-down, 39
Morning warm-up, 39
Occupancy modes, 36
Outdoor/return air, 43
Peer-to-peer communication, 48
Power-up sequence, 35
Random start, 35
Smart reset, 49
Timed override control, 37
Two-pipe operation, 43
Two-position damper control,
46
Two-position valve operation,
43
Unit protection strategies, 48
Valves, 42
Zone temperature control, 38
Service pin button, 51, 56
Smart reset
Diagnostic, 49, 59
Unit protection, 49
Specifications
AC power wiring, 7
Agency listing/compliance, 3
Clearances, 2
Dimensional diagram, 3
Dimensions, 2
Input/output terminal wiring, 7
LonTalk communication wiring
and addressing, 9
Storage environment, 2
Transformers, 8
Status indicators for operation and
communication
Diagnostics, 58
General, 51
Green (status) LEDs, 57
LEDs, 51
Manual output test, 52
Red (service) LEDs, 56
Service pin button, 56
Test button, 51
Yellow (communication) LEDs,
57
Storage environment, 2

Index

Switching devices
Condensate overflow, 4, 14
Current sensing, 4
Fan status, 4
Freeze protection, 4, 14
Low-coil-temperature, 4
Occupancy, 4, 15

T
Temperature sensors
Table of options, 5
Water and duct, 4
Zone, 4
Termination resistors, 9

Valves
Actuators, 4
Calibration of modulating, 42
Four-pipe operation, 43
General operation, 42
Isolation-valve operation, 43
Operation of modulating, 42
Operation of two-position, 43
Supported applications, 1, 21,
42
Tri-state modulating, 1, 21, 42
Troubleshooting, 64
Two-pipe operation, 43
Two-position, 1, 21

Zone humidity
Sensor, 5
Zone temperature
Input, 16
Sensors, 4
Zone temperature control, 38
Zone temperature failure
diagnostic, 59

Test button, 51–52
Timeclock, 15

Timed override control, 37
Transformers, 4, 7, 8
Troubleshooting
DX cooling, 65
Electric heat failure, 65
Fans, 63
Outdoor air damper, 66
Valves, 64
Two-pipe operation, 43
Two-position damper control, 46
Two-position valve operation, 43
Types of diagnostics, 58

U
UL, see Agency listing/compliance
Unit protection strategies
Condensate overflow, 49
Discharge air temperature low
limit, 50
Fan off delay, 49
Fan status, 49
Filter-maintenance timer, 50
Freeze avoidance, 50
Freeze protection, 50
Low-coil-temperature
protection, 49
Smart reset, 49
Unit ventilators, 1, 21
Universal 4–20 mA, 19

Water and duct temperature
sensors, 4
Wiring
BAS communication, 9
Compliance with National
Electrical Code, 7, 8, 9
General, 7–9
Input/output terminals, 7
LonTalk communication, 9
Minimum requirements, 22
Requirements and options,
22–34
Wiring diagrams, 22–34
Electric heat unit, 30
Electric heat unit with DX
cooling, 29
Four-pipe heating/cooling unit
with auto changeover, 27
Four-pipe heating/cooling unit
with face-and-bypass damper,
33
Four-pipe hydronic heating/
cooling unit, 26
Two-pipe heating unit with DX
cooling, 28
Two-pipe heating/cooling unit
with face-and-bypass damper,
32
Two-pipe hydronic heating/
cooling unit with auto
changeover, 25
Two-pipe hydronic-cooling unit,
23
Two-pipe hydronic-heating unit,
24

CNT-SVX07C-EN

Trane
A business of American Standard Companies
www.trane.com
For more information contact your local Trane
office or e-mail us at comfort@trane.com

Literature Order Number

CNT-SVX07C-EN

File Number

SV-ES-BAS-CNT-SVX-07C-EN 0405

Supersedes

CNT-SVX07B-EN October 2001

Stocking Location

Inland

Trane has a policy of continuous product and product data improvement and reserves the right to
change design and specifications without notice. Only qualified technicians should perform the installation and servicing of equipment referred to in this publication.

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