Dometic Heat Pump will not stay in cool mode

[johnsonbert]

My Dometic heat pump will not stay in cool mode. After running for about 3-4 minutes in cool, it reverts to heat mode. I checked the solenoid for tightness and it seemed fine. I did not yet check the resistance on the coil itself as I did not want to disassemble the wiring yet. It appears that one wire form the solenoid goes to the circuit board and it appears by the wiring diagram that the other goes to a post on a start capacitor. Is there a way to narrow down the possibilities of either the solenoid, capacitor, or circuit board. All other functions seem normal, except for the solenoid releasing the reversing valve. It appears the reversing valve is working as it is supposed to. Thanks in advance for any suggestions you may have. We are on the road so may be a tough fix as we will not be in any location long enough to order a part. Thanks again for the help. Bert

[johnsonbert]

Put the coil on this morning. It has run correctly for the last 3 hours. Thanks to all for the help and suggestions and thanks again to William Hendrix for the diagnosis assistance and sending out the part. I highly recommend William for AC questions related to the older Dometic units. Thanks again to all, Happy Trails Bert

[dougrainer]

If it is NOT the electrical solenoid, then the HP must be replaced. You cannot replace the Copper tubed valve as they do not offer it. The good news is, the NEW Dometic HP's were redesigned to COOL when the reversing valve circuit fails. Doug

PS, the electric solenoid kit comes with 2 solenoids(different solenoids). Dometic packages 2 different solenoids because they are not sure which models had which type solenoids.

[johnsonbert]

In further discussion, the solenoid would let the reversing valve revert to heat after 3-4 minutes, but there was still 110 volts at the board where the solenoid connects. So we will try a reversing valve solenoid, have it coming. Thought seriously about pulling one out of one of the others, but temps in the mid 90's today and no shade, so did not seem like a good thing to do. Did the diagnosis and testing before 10:30 so it was not to bad. The gent that Ivylog steered me to was very knowledgeable and was thinking that the board would still be good, we also did a a reset of the wall thermostat. Thanks for the help and suggestions and will let you know how it comes out when the part arrives. Thanks again for the responses, Happy Trails Bert

[DSDP_Don]

"johnsonbert"...I had a 2005 Monaco Diplomat with the Dometic heat pumps and had the same issue. On mine it was the reversing valve. If you get the long model number off of the unit, you can go to PPL Parts, go to their Dometic A/C section and then look for your model number. They list all of the parts for your A/C unit. I bought the reversing valve and a new start capacitor, since mine was crushed by the clamp when Dometic installed it. The reversing valve fixed the issue. As stated above, the default is Heat Pump and when the reversing valve quits, it won't kick it over to A/C. It's a very simple replace.

If you don't trust the diagnosis, pull the reversing valve off of one of your other A/C units and swap it out. It's a single bolt and long wire with a spade connector. Don't forget to ground the capacitors before playpng/touching any of the connections.

[Ivylog]

Very interesting... I would put 120V straight to the solenoid and see what happens. While 120V is not as bad as 12V being metered, but not enough amps to pull a solenoid in, it is a possibility once the relay on the board warms up.

[johnsonbert]

Thanks for the contact information, I have been in touch with him and we are working on it. The thermostat seems to be OK and the board continues to put out 110 after the solenoid kicks off, so it may be the solenoid itself checking out after a few minutes. Thanks again for the contact info. Happy Trails Bert

[Ivylog]

That vintage Duo Therm reverts to heat when there is no 120 V to the solenoid. Some solenoid ihave a plug where you can pull it off check the ohms and the voltage very easily. It sounds like your circuitboard stops putting 120 V to the solenoid after a few minutes.

I recently had much the same problem so I jumpered 120V to the solenoid wire off of the circuit board from the 120V to the board to get our unit to cool until I can get a new board. I posted a link to the person I bought a rebuilt circuitboard from because there are no new ones available so search under Ivylog and eBay in the last two weeks. He is in Boulder Colorado and will ship immediately.
*Here's his #
303-809-6006