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