Heat pump problem

[us71na]

I have a 2011 Jayco Skylark with the standard Dometic heat pump they came with. Last fall we went camping late enough in the year that we needed to use the heat instead of the A/C. I sent the temp where we wanted it and put the thermostat in heat mode and the unit started and warmed the trailer up nicely. Once it reached the temp setting the unit shut off. A while later, when the temperature in the trailer had dropped, the heat pump clicked, the fan ran for 1/2 second and stopped, ran for 2 seconds and stopped, then 5-10 seconds and stopped, 20 seconds and stopped and finally started and ran until the temp set point was reached. When the trailer cooled a bit again it did the same start stop routine. It continued doing this hesitant start thing throughout the night and into the next day until we left. Some times it would start and stop 2-3 times and other times it would take 4-5 false starts before it would run.

It does not do the false start thing in cooling mode. If you move the temperature setting up a couple of degrees, it will immediately start up and run until the temp is reached. Voltage in the trailer was 123 volts on my digital voltmeter.

My local dealer has been unable to solve the problem. He replaced the thermostat with a new one and it still does the same thing.

[12VOLTMAN]

If moving the temp setting up a couple of degrees gets rid of the false start, I would say the thermostat contacts are the issue for some reason. A heat pump works exactly the same in heating as it does in cooling except that the reversing valve shifts position. So, it shouldn't be anything in the unit causing it or it would false start in cooling mode as well. But, since you have a new stat I would think that would have fixed it. If it were me I think I would look in the heat pump and see what exactly gets energized when you call for heat. If it's a relay, change it. Maybe the coil is getting weak and for some reason it hesitates in cooling. Relays are usually cheap so it's worth a try.

[rryman]

When the fan shuts off for that brief period, can you still hear the compressor running? I don't think the compressor would restart that quick after starting. When my unit at home comes on, the fan dosen't start up on high right away, but delays a bit until the coil temp gets warm enough that it won't blow cold air. It sounds like there may be a coil thermostat cutting the fan off until the temp builds up in the coil. This is pure speculation of course, but if it isn't the thermostat, maybe this is something new. IF the compressor is also short-cycling, I would be concerned, as it will shorten the life of the compressor.

[us71na]

The thermostat is Dometic digital and there are no contacts.

The compressor doesn't/won't start until the fan is up to speed. Once the fan is running at speed the compressor will start and run until the temp setting is reached. Then everything shuts off.

The reversing valve is only energized in the heat mode, but it stays energized the entire time it is in heat mode, even when the fan is not running. I'm suspecting that the valve coil is pulling down the 12 volt circuit so the relay doesn't get full voltage.

I've asked the local dealer to call Dometic several times, but so far they have been reluctant to do that and Dometic won't talk to me, they refer me to my dealer.

[us71na]

After multiple weeks (6) and trips to the local Jayco dealer, I contacted Dometic customer service. Neither the dealer nor Dometic could solve the problem with my heat pump unit so it was replaced by Dometic.

I had asked the dealer early on to contact Dometic and instead they relied upon their own "expertise" which was unable to locate the problem. They replaced the thermostat and a circuit board which did not solve the problem. After threatening to take my trailer elsewhere and my call to Dometic, it was finally determined that the heat pump should be replaced. The new unit starts and operates normally.

My thanks to Rhonda at Dometic for taking care of this problem for me.