Originally Posted by gljurczyk
More then likely what you are hearing is the unit going into defrost mode. The condenser fan will shut off and reverse cycle for about 3 to 5 mins. then it kicks back on, you need to let it do that. The colder outside the more it will happen. The unit coils builds ice and it has to defrost them to start working again
Thanks!!! I never thought of that. Dr Google found this info about "RV Heat Pump Defrost Mode:
"Defrost Cycle: During heat pump operation, if the outside coil begins to freeze up, a defrost cycle is initiated that temporarily puts the heat pump back into air conditioning mode. This reverses the refrigerant flow and melts the ice forming on the outside coil. Typically this occurs when the outside temperatures are below 42 °F and repeats every 25 minutes of compressor run time as long as the outside temperature stays below 42 °F and above 30 °F. Therefore, during this period of operation you, (the user) will temporarily feel cold air inside the RV at the registers. This is normal and is NOT an indication of malfunction. (Note: Defrost cycling shall continue until the measured temperature of the Outdoor Sensor is ≤30 °F or ≥42 °F.)"
And this: "The heat pump also goes into periodic defrost cycles at colder temperatures. You will hear the inside fan stops, but the compressor keeps humming for a couple of minutes, then the inside fan starts again".