AC/heat pump runs continuously unless shut off manually

[lsinclair]

On an '08 Classic 30' with one 15K Duo Therm Dometic Penguin AC running, the unit fails to cycle/shut off when desired set temp is attained. It continues to run. Unit cools fine.
Likewise when heat pump is selected and temp set, it also continues to run. Heats fine.
Furnance function normal.
Additionally, on two separate occasions, the electric control unit display went blank, no response.Manually turning the switch to off and after letting it set for a period of time, the display and functions started working as normal when manually switched on.
There is no problem with cold or hot air in the selected mode. Problem appears to be within control circuit board.
Any advise/troubleshooting tips would be sincerely appreciated.
Thanks, Larry

[Pahaska]

Sounds like your thermostat may be going on the blink.

The thermostat connects to the AC with a 4-conductor telephone cord. The outer two conductors are 12v and ground. The inner two conductors carry serial commands Kinda like a USB port on the computer.

The AC/HP is initially in heat pump mode. The fact that it starts and switches to AC shows that the connection is good and the circuit board in the AC/HP can receive and decode commands.

I would check that both ends of the telephone cable are plugged in firmly. The display going blank could be a loose connection since the 12v comes from the AC/HP.

If the connections are good, I think the thermostat may have problems. From the fact that it blanks out, I suspect that the rudimentary processor in there may be hanging up.

There is a thermostat reset sequence using the buttons that the Dometic Tech showed me, but I don't remember it and my papers are all in the trailer 10 miles away. Maybe someone else can supply the sequence.

[lewster]

Dometic Comfort Control Center (CCC) reset procedure:

Turn CCC off at bottom switch.

Press and hold the top and bottom buttons on the CCC

Turn the CCC on at the bottom switch

Release the 2 buttons

You should see 'FF' in the window.

If you get nothing or 'EE' you either have a 12VDC power supply problem or a communication problem from the CCC to the upper unit in the A/C

[lsinclair]

Thanks for the info Lew. I checked it and 'FF' is displayed. I had to stop at that point as I heard a hissing noise and discovered my W/H was leaking at the thermostat fitting. Examining the electric heating element, the threads on both the element and tank threads appear in good shape. Nevertheless, it is still leaking. I didn't have a large enough socket to properly tighten the element nor did I have another rubber gasket (existing one looks good).
What size socket fits the hex on the element and is their a torque value?

I had a job transfer to Salmon ID and temporarily living in my AS and the vast majority of my tools are in CO, so naturally that is when problems typically arise.
Thanks again for the help, Larry