Trane Heat Pump time delay between OD fan cut on and solenoid deenenergizing

by Thomas
(Elkton, Virginia)

I have a Trane TWR736A100A1 heat pump. At the conclusion of the defrost cycle, the defrost control board has a time delay between the OD fan cut on and the reversing valve solenoid deenenergization. In temperatures below 34 degrees, this delay causes the head pressure to drop, causing the reversing valve to hang in cool position after the defrost is complete. The charge is chart perfect. The coils are spotless. The TEX used in heat pump mode is fed with 14 degree subcooled liquid. The superheat is variable from 2 degrees (at 20 degrees outside) to 25 degrees (at 50 degrees outside). I suspect if I could have the OD fan and the solenoid act at the same time the reversing valve would switch correctly. The control board for this unit has no adjustments at all. Any ideas to help??

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