Trane 4WCY4036B3 Installation And Operation Manual page 23

Table 12. Demand Defrost Control Checkout Table (continued)
SYMPTOMS
Defrost initiates on
8. approximately 30/45 minute
intervals.
OD fan runs during defrost.
9.
No SOV delay on defrost
10.
termination.
11. ODS-A burned out.
On SCROLL bearing units,
12.
compressor does not operate.
13. On SCROLL bearing units, no 30
second off delay at defrost
initiation.
18-BB34D1-19B-EN
CHECKS
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?
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
Y Remove short.
Replace defective sensor (Clear coil and re
N
gency heat light).
Complete SYMPTOM #3.
Y
Adjust as needed.
Replace defrost control.
N
See SYMPTOM #9.
Replace if necessary.
Replace defrost control.
The soft-switch time is defeated when J1 is
Y
cut.
Replace defrost control.
N
Check low voltage wiring for miswire.
Y
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.
N
U U n n i i t t S S t t a a r r t t u u p p
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