Carrier 38MGQ Series Service Manual page 64

The cooling operation or heating operation does not operate.
Supposed causes
S 4- -way valve faulty
Check the 4- -way valve. Refer to part 5 in 9.5.
When cooling, heat exchanger of non- -operating indoor unit frosts.
When heating, non- -operating indoor unit gets warm.
Supposed causes:
EXV faulty
S
S Wire and tubing connected in reverse
Check the EXV. Refer to part 6 in 9.5 Trouble Criterion Of Main Parts.
IMPORTANT: If you replace outdoor main PCB, you need to check whether the PCB is produced before Apr. 2013. If yes, you need
to short connect OLP connector. Otherwise, the outdoor LED displays "P0".
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