DEMAND DEFROST CONTROL CHECKOUT

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?

 

 

Page 17

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Trane WCY024G1, WCY042G1, WCY048G1, WCY036G1, WCY030G1 manual Demand Defrost Control Checkout, Symptoms Checks YES/NO Actions
Page 16 Page 18

WCY036G1, WCY042G1, WCY060G1, WCY048G1, WCY030G1 specifications

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