White Rodgers 21V51U 843 Universal Two Stage Hsi Integrated Furnace Control Kit Wiring Diagram 81 Of Rodgers_catalog_R 4425_

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INTEGRATED
FURNACE CONTROLS

21V51U-843 WIRING
AND CONFIGURATION

The 50V51-843 has only one serviceable part –an automotive
type fuse, which protects the low voltage transformer from damage if the output is short-circuited. If the fuse has opened up,
remove whatever caused the short circuit and replace the fuse
with only a 3 amp automotive type fuse. If the fuse is not the

Following installation or replacement, follow appliance manufacturer’s recommended installation or service instructions to
insure proper operation.

50V51-843 TYPICAL SYSTEM WIRING DIAGRAM

NEUTRAL
(LINE)

120 VAC
24 VAC CLASS II
TRANSFORMER
TH

24 VAC

TR

50V51-843
CIRC.
CIRCULATOR INTERFACE

LINE
XFMR
EAC
HUM
IGN
IND HI
IND LO
IND N
IGN N

INDUCER
HUMIDIFIER
(OPTIONAL)

CIRC N
HUM N
LINE N
XFMR N
EAC N

ELECTRONIC
AIR CLEANER
(OPTIONAL)

THERMOSTAT

IGNITOR

R

R

G

G

W2

W2

W1

W1

Y2

Y

Y

YLO
DEHUM

CONDENSING
UNITS

B/C
O

FLAME
SENSOR
PROBE

E2

HLO
HLI
FP
PS1
MVL
MVH
GND
GND
PS2
MV COM
TR
TH

HIGH LIMIT ROLLOUT
(N. C.) SWITCH (N. C.)

1ST STAGE PRESSURE
SWITCH (N. O.)

AUX. HIGH
LIMIT (N. C.)

LEGEND
Low Voltage (24 VAC)
GAS
VALVE

Line Voltage (120 VAC)
N.C. = Normally closed switch
N.O. = Normally closed switch

2ND STAGE PRESSURE
SWITCH (N. O.)

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181

TECHNICAL HELP

HOT
(LINE)

cause of the control’s problem, replace the entire 50V51-843
control. There are no other user serviceable parts.

21V51U-843
OPERATION

INTEGRATED
FURNACE CONTROLS
TRI-COLOR (DSI LED) DIAGNOSTIC TABLE

Green
LED
Flash

Amber Red LED
Error/Condition
LED
Flash
Flash
1
Flame sensed when no flame should be present

Pressure switch stuck closed/ inducer error

Pressure switch stuck closed. Check switch function, verify inducer is turning
off.

3
4
5
6

1st-stage pressure switch stuck open/inducer
error
Open limit switch
Open rollout/open fuse detect
1st-stage pressure switch cycle lockout

7

External lockout (retries exceeded)

8

External lockout (ignition recycles exceeded
where flame is established and then lost)
Grounding or Reversed polarity

Check pressure switch function and tubing. Verify inducer is turning on the
pulling sufficient vacuum to engage switch.
Verify continuity through rollout switch circuit.
Verify continuity through rollout switch circuit, check fuse.
If the first stage pressure switch cycles 5 times (open, closed) during one call
for heat from the thermostat the control will lockout. Check pressure switch
for fluttering, inconsistent closure or poor vacuum pressure.
Failure to sense flame is often caused by carbon deposits on the flame
sensor, a disconnected or shorted flame sensor lead or a poorly grounded
furnace. Carbon deposits can be cleaned with emery cloth. Verify sensor is
not contacting the burner and is located in a good position to sense flame.
Check sensor lead for shorting and verify furnace is grounded properly.
Check items for exceeded retries listed above and verify valve is not
dropping out allowing flame to be established and then lost.
Verify the control and furnace are properly grounded. Check and reverse
polarity (primary) if incorrect.
Verify valve is not receiving voltage from a short. If a valve wiring is correct
and condition persists, replace module.
Possible blower failure, restricted air flow through appliance or duct work.
Verify continuity through limit switch circuit and correct overheating cause.
Fault code indicates the module ignitor contacts are not functioning properly.
Replace module.
Module contacts for gas valve not operating or processor fault. Reset control.
if condition persists replace module.
Check pressure switch function and tubing. Verify inducer is turning on and
pulling sufficient vacuum to engage switch.
Normal operation - first stage
Normal operation - first stage
Second stage call for heat on thermostat circuit with no call for first stage.
Verify DIP switches are set for two stage thermostat and check thermostat
first stage circuit. Configured for a multi-stage thermostat the Module will not
initiate heating unless first stage call from thermostat is received.
Module will allow cooling to operate with only a "Y signal from the thermostat
but will also trigger this code. Verify thermostat is energizing both "Y" and "G"
on call for cool. Check "G" terminal connections.
Low flame sense current is often caused by carbon deposits on the flame
sensor, a poorly grounded furnace or a mis-aligned flame sense probe.
Carbon deposits can be cleaned with emery cloth. Check for improve
furnace and module ground. Verify sensor is located in or very near flame as
specified by the appliance manufacturer.
Normal operation. Waiting for call from thermostat or receiving thermostat
call for cool.

10
11
12
Solid
3
double

Module gas valve contacts energized with no
call for heat
Limit switch open – possible blower failure
overheating limit
Module Ignitor contact failure
Module - internal fault condition

1
2
3

2nd-stage Pressure Switch Stuck Open/Inducer
Error
Normal Operation with call for first stage heat
Normal Operation with call for second stage heat
W2 present with no W1

4

Y present with no G call

Rapid

Low flame sense current

Standby or Call for Cool

DIAGNOSTIC FEATURES

TECHNICAL HELP

Verify the gas valve is operating and shutting down properly. Flame in burner
assemble should extinguish promptly at the end of the cycle. Check orifices
and gas pressure.

2

9

1

Comments/Troubleshooting

air flow designated by the furnace manufacturer. Consult the
furnace manufacturer for flash code detail.

The control continuously monitors its own operation and the
operation of the system. If a failure occurs the diagnostic indicator LED (DSI) will flash a “RED” failure code. If a failure
is internal to the control the “RED” indicator will stay on
continuously. In this case, the entire control should be
replaced as the control is not field-repairable. If the LED is
continuously OFF, there may be no power to the control or a
failure within the control. If the sensed failure is in the system
(external to the control), the LED will flash RED in the sequence
listed in the Diagnostic Table. The LED will also indicate “System
Status” as per the Amber and Green LED signatures listed in the
Diagnostic Table. The LED will flash one RED flash at power up.

To retrieve fault codes, push and release the “LAST ERROR”
button for more than 1/5 second and less than 5 seconds.
(Control will indicate this period by solid GREEN for 1/5 secs.
to 5 secs.). The LED will flash up to five stored fault codes,
beginning with the most recent. If there are no fault codes in
memory, the LED will flash two green flashes. The control will
flash the most recent error first and the oldest error last (last in
first out). There shall be 2 seconds between codes. Solid LED
error codes will not be displayed.

CFM INDICATOR

NOTE

The LED (DS2) CFM flashes when the blower motor is running.
The flashing indicates the motor CFM (cubic feet per minute)  
182

FAULT CODE RETRIEVAL

These error codes may be different from furnace label or
furnace manual.

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