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DIAGNOSTIC FEATURES

The control continuously monitors its own operation and the

operation of the system. If a failure occurs the diagnostic in-

dicator 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 theAmber and Green LED signatures listed in the

Diagnostic Table. The LED will flash one RED flash at power up.

CFM INDICATOR

The LED (DS2) CFM flashes when the blower motor is running.

The flashing indicates the motor CFM (cubic feet per minute)

INTEGRATED

FURNACE CONTROLS

21V51U-843

OPERATION

TRI-COLOR (DSI LED) DIAGNOSTIC TABLE

Green

LED

Flash

Amber

LED

Flash

Red LED

Flash

Error/Condition

Comments/Troubleshooting

1 Flame sensed when no flame should be present

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 Pressure switch stuck closed/ inducer error

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

off.

3 1st-stage pressure switch stuck open/inducer

error

Check pressure switch function and tubing. Verify inducer is turning on the

pulling sufficient vacuum to engage switch.

4 Open limit switch

Verify continuity through rollout switch circuit.

5 Open rollout/open fuse detect

Verify continuity through rollout switch circuit, check fuse.

6 1st-stage pressure switch cycle lockout

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.

7 External lockout (retries exceeded)

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.

8 External lockout (ignition recycles exceeded

where flame is established and then lost)

Check items for exceeded retries listed above and verify valve is not

dropping out allowing flame to be established and then lost.

9 Grounding or Reversed polarity

Verify the control and furnace are properly grounded. Check and reverse

polarity (primary) if incorrect.

10 Module gas valve contacts energized with no

call for heat

Verify valve is not receiving voltage from a short. If a valve wiring is correct

and condition persists, replace module.

11 Limit switch open – possible blower failure

overheating limit

Possible blower failure, restricted air flow through appliance or duct work.

Verify continuity through limit switch circuit and correct overheating cause.

12 Module Ignitor contact failure

Fault code indicates the module ignitor contacts are not functioning properly.

Replace module.

Solid Module - internal fault condition

Module contacts for gas valve not operating or processor fault. Reset control.

if condition persists replace module.

double

2nd-stage Pressure Switch Stuck Open/Inducer

Error

Check pressure switch function and tubing. Verify inducer is turning on and

pulling sufficient vacuum to engage switch.

Normal Operation with call for first stage heat

Normal operation - first stage

Normal Operation with call for second stage heat Normal operation - first stage

W2 present with no W1

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.

Y present with no G call

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.

Rapid

Low flame sense current

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.

Standby or Call for Cool

Normal operation. Waiting for call from thermostat or receiving thermostat

call for cool.

air flow designated by the furnace manufacturer. Consult the

furnace manufacturer for flash code detail.

FAULT CODE RETRIEVAL

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.

NOTE

These error codes may be different from furnace label or

furnace manual.

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