Demand Defrost Control Checkout - Trane WCY024G1 Installation, Operation & Maintenance Manual

DEMAND DEFROST CONTROL CHECKOUT

SYMPTOMS
1. LED off.
2. LED flashing very rapidly (greater
than 4 times/sec) or appears to be on
continuously.
3. Control does not initiate a normal
defrost.
4. Control does not initiate a forced
defrost.
5. Defrost initiates manually but terminates in less than 10 seconds.
6. Defrost initiates manually but
terminates on time.
7. Defrost initiates on approximately
15/25 minute intervals.
8. Defrost initiates on approximately
30/45 minute intervals.
9. OD fan runs during defrost.
10. No SOV delay on defrost
termination.
11. ODS-A burned out.
12. On SCROLL bearing units,
compressor does not operate.
13. On SCROLL bearing units, no 30
second off delay at defrost initiation.
CHECKS
1. 24V R-B & Y-B at board, with unit running?
2.Short FRC_DFT pin to TEST_COMMON pin.
Is defrost cycle initiated?
TEST_COMMON pin shorted to TST pin?
OD Temp. below 49°F.
OD Coil temp. below 35°F.?
"Delta" T increasing?
1. LED flashing?
2. Check for 24V Y-B at board with unit running.
3. Check sensors for correct mounting
(connection) and resistance.
4. Short FRC_DFT pin to TEST_COMMON pin.
Is defrost cycle initiated?
24V R-B & Y-B at board with unit running?
1. Coil sensor circuit open or reading at a very
high resistance?
2. Does OD fan cycle off in defrost?
3. Windy weather preventing normal
termination?
Be sure OD coil is clean.
1. Coil sensor open or reading a very
high resistance?
2. Ambient sensor reading less than normal?
3. OD fan off in defrost?
1.TEST_COMMON pin shorted to TST pin?
2. Do both sensors check OK?
3. Verify correct system charge.
4. Verify a "forced defrost" terminates less than
15 minutes.
5. OD fan motor off in defrost.
6. Verify proper SOV operation.
Has J1 been cut?
1. B to T greater than 10 volts?
1. 24V R-B at board & 24V Y-B at board?
2. Check protective devices in YO circuit . 24V
YO-B present after 30 seconds.
Check voltage between control terminals 2 and
7,force a defrost cycle. Is 24V present for 30
seconds and 0V thereafter?
YES/NO ACTIONS
N Repair low voltage wiring.
Y Complete Check #2.
N Replace defrost control.
Y LED is bad but control will still function.
Y Remove short.
N Replace defrost control.
Check refrigerant circuits for balanced
N distribution of refrigerant if OD coil is
frosting and delta T is not increasing
N Refer to SYMPTOM #1.
Y Complete Check #2.
N Repair low voltage wiring.
Y Complete Check #3.
Remount or replace sensor if necessary.
N Replace defrost control.
Y Y-B signal or control may be intermittent
N Repair low voltage wiring.
Y Replace defrost control.
Replace defrost control.
Y Replace coil sensor.
N Replace defrost control.
N Complete Check #2.
Y Replace coil sensor.
N Complete Check #3.
Y Replace ambient sensor.
N Replace defrost control.
Y Remove short.
Replace defective sensor (Clear coil and
N
reset Emergency heat light).
Y Complete SYMPTOM #3.
Adjust as needed.
N Replace defrost control.
See SYMPTOM #9.
Replace if necessary.
Replace defrost control.
The soft-switch time is defeated when J1
Y
is cut.
N Replace defrost control.
Y Check low voltage wiring for miswire.
N Check for short in low voltage wiring.
N Repair low voltage wiring.
N Y-B signal or control may be intermittent
N Replace defrost control.
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