Trane WCY024G1, WCY042G1, WCY048G1 Demand Defrost Control Checkout, Symptoms Checks YES/NO Actions

SYMPTOMS

CHECKS

YES/NO

ACTIONS

1. LED off.

1. 24V R-B & Y-B at board, with unit running?

N

Repair low voltage wiring.

Y

Complete Check #2.

2.Short FRC_DFT pin to TEST_COMMON pin.

N

Replace defrost control.

Is defrost cycle initiated?

Y

LED is bad but control will still function.

2. LED flashing very rapidly (greater

Y

Remove short.

than 4 times/sec) or appears to be on

TEST_COMMON pin shorted to TST pin?

continuously.

N

Replace defrost control.

3. Control does not initiate a normal

OD Temp. below 49°F.

Check refrigerant circuits for balanced

defrost.

OD Coil temp. below 35°F.?

N

distribution of refrigerant if OD coil is

"Delta" T increasing?

frosting and delta T is not increasing

1. LED flashing?

N

Refer to SYMPTOM #1.

Y

Complete Check #2.

2. Check for 24V Y-B at board with unit running.

N

Repair low voltage wiring.

Y

Complete Check #3.

3. Check sensors for correct mounting

Remount or replace sensor if necessary.

(connection) and resistance.

4. Short FRC_DFT pin to TEST_COMMON pin.

N

Replace defrost control.

Is defrost cycle initiated?

Y

Y-B signal or control may be intermittent

4. Control does not initiate a forced

N

Repair low voltage wiring.

defrost.

24V R-B & Y-B at board with unit running?

Y

Replace defrost control.

5. Defrost initiates manually but terminates in less than 10 seconds.

Replace defrost control.

6. Defrost initiates manually but

1. Coil sensor circuit open or reading at a very

Y

Replace coil sensor.

terminates on time.

high resistance?

2. Does OD fan cycle off in defrost?

N

Replace defrost control.

3. Windy weather preventing normal

termination?

7. Defrost initiates on approximately

Be sure OD coil is clean.

N

Complete Check #2.

15/25 minute intervals.

1. Coil sensor open or reading a very

Y

Replace coil sensor.

high resistance?

2. Ambient sensor reading less than normal?

N

Complete Check #3.

Y

Replace ambient sensor.

3. OD fan off in defrost?

N

Replace defrost control.

8. Defrost initiates on approximately

1.TEST_COMMON pin shorted to TST pin?

Y

Remove short.

30/45 minute intervals.

N

Replace defective sensor (Clear coil and

2. Do both sensors check OK?

reset Emergency heat light).

Y

Complete SYMPTOM #3.

3. Verify correct system charge.

Adjust as needed.

4. Verify a "forced defrost" terminates less than

N

Replace defrost control.

15 minutes.

5. OD fan motor off in defrost.

See SYMPTOM #9.

6. Verify proper SOV operation.

Replace if necessary.

9. OD fan runs during defrost.

Replace defrost control.

10. No SOV delay on defrost

Y

The soft-switch time is defeated when J1

termination.

Has J1 been cut?

is cut.

N

Replace defrost control.

11. ODS-A burned out.

Y

Check low voltage wiring for miswire.

1. B to T greater than 10 volts?

N

Check for short in low voltage wiring.

12. On SCROLL bearing units,

1. 24V R-B at board & 24V Y-B at board?

N

Repair low voltage wiring.

compressor does not operate.

2. Check protective devices in YO circuit . 24V

N

Y-B signal or control may be intermittent

YO-B present after 30 seconds.

13. On SCROLL bearing units, no 30

Check voltage between control terminals 2 and

second off delay at defrost initiation.

7,force a defrost cycle. Is 24V present for 30

N

Replace defrost control.

seconds and 0V thereafter?