Heat Pump Hum / Fan Kick Off or to Low

[Joseph Carozzoni]

We took delivery of a 2014 Sunseeker in July 2013 and opted for the 15K Heat Pump. In fall 2013 and spring 2014 it keep the coach at 60 degrees in mid-to-low 30F temperatures. The last two trips in fall 2014, in the middle of the night the fan would stop (or switch from high to low – not sure) and the Heat Pump sounded like a hum. Both times we turned it off for an hour, then back on and it worked until we turned if off in the morning. Any ideas what is going on here?

[Witch Doctor]

Originally Posted by Joseph Carozzoni

We took delivery of a 2014 Sunseeker in July 2013 and opted for the 15K Heat Pump. In fall 2013 and spring 2014 it keep the coach at 60 degrees in mid-to-low 30F temperatures. The last two trips in fall 2014, in the middle of the night the fan would stop (or switch from high to low – not sure) and the Heat Pump sounded like a hum. Both times we turned it off for an hour, then back on and it worked until we turned if off in the morning. Any ideas what is going on here?

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

[Joseph Carozzoni]

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".

[RamblerGuy]

The instructions for the Dometic thermostat on our 2011 year model 3100 describes the defrost cycle as stated above. In addition, it says the thermostat automatically shuts off the heat pump and runs the gas furnace if the outside temperature drops below 30 F. Your thermostat may work a little differently.

[Joseph Carozzoni]

Thanks - but no such luck. We've got the Single Zone LCD Thermostat that simply shuts off the Heat Pump below 30F.

I've noticed Dometic makes some more advanced thermostats, including one that has a LED to show the Heat Pump is in Defrost Mode. I'm going to look into upgrading our thermostat.