Dometic thermostat has no power

[Mbstrustee]

Thermostat will not come on. Appears no power going to it. Checked breakers and fuses. Appears to be ok. Electricity ok to rest of trailer. Tried a reset on thermostat nothing happened. Any advise?

[BayouBiker]

I presume it is the CCC2 thermostat controller. It is powered through the RJ-14 (4 wire phone like) communications cable. Two of the wires are 12V +/- the other pair is for communication. The roof unit uses 12V power for the control circuits and 120VAC for the compressor and fans.

So the 12V fuse could be the issue, or a problem with the batteries or 12V system or the Store/Use switch and solenoid or the Heat Pump controller board in the roof unit, or the previously mentioned communication cable or the CCC2 unit itself.

Check the 12V system first and recheck the 12V fuses. If you're handy with a multimeter let me know and we can go from there.

[Jim Flower]

Try messing with the telephone connector that is located under the interior access to the air conditioner. The cowl is removed by taking out 6 screws. Once removed, the connector is exposed and you may see that the cables that are plugged into the connector are not secure in their place. The cables connect the thermostat with the AC unit controller. That is my only experience with the issue. Good luck. Jim

[BayouBiker]

His is a ducted system so the phone connectors are in the air intake plenum behind the intake filter screens, also easy to access. If he has a single Heat pump there will be a spare one for daisy chaining to other devices plus the one connected to the CCC2.

[Jim Flower]

Better than the old system in mine. Jim

[Jim Flower]

It could also just be the connection on the back of the CCC2 is loose. Jim

[Mbstrustee]

Thanks to all. It is ccc2 thermostat. AC is duel air. I checked our batteries and they are fully charged. I checked the fuses and breakers. I’ve checked the telephone like connections on the thermostat and up in the air intake. Thermostat still dark. Everything else electrical is working except the fantastic fan.

[Jim Flower]

Nasty! Way beyond me. I usually “ fix” electrical stuff by giving it a slap on the side. Jim

[bradt]

I think the Fantastic Fan also not working is a clue.
It could be the Fan and the control board in the A/C unit get their 12vdc thru the same wiring in a daisy chain fashion.
Since all the basic checks on the A/C haven't resolved the problem, shift gears and trouble shoot the Fantastic Fan.
Also, since more than 1 item is affected, check fuses again, just in case you could have missed it there.
Good luck!
Brad

[LAWBC]

Have you tried the old tried method and unplug the trailer from shore power then switch battery to "Store" .Then fire up again in effect rebooting

[Mbstrustee]

Problem solved. The power connection on the battery for the thermostat was loose. Cleaned and snugged it up and it came on and the AC is now running fine. Fantastic fan still not working though. Thanks for all you suggestions.

[Al and Missy]

On my 12V circuit breakers a trip was not obvious. Further, pushing the reset with a finger didn't work. I had to get a small pointed object (stylus, toothpick, ballpoint pin, etc) to push the reset button far enough for it to work.

Al

[BayouBiker]

Originally Posted by Mbstrustee

Problem solved. The power connection on the battery for the thermostat was loose. Cleaned and snugged it up and it came on and the AC is now running fine. Fantastic fan still not working though. Thanks for all you suggestions.

Good to hear you resolved the thermostat and heap pump power issue. The fan has a separate low amp fuse in the fan body to protect it from a rain caused short, it is easy for it to blow. The fan is generally on the same circuit as the Heat pump control power so a loose connection could cause low voltage to the fan inducing high current an the blown fuse. Also the 12V power feed wires are easy to access and check for power by removing the trim.

[shb2777]

I just replaced mine. The jack on the back of the board had pulled loose and broke one of the contact prongs on the board itself. No way to fix it had to replace. Hope this helps.
Thanks Steve

[Jim Flower]

Originally Posted by Jim Flower

It could also just be the connection on the back of the CCC2 is loose. Jim

Mbstrustee

Is this the connection that you are referring to that resolved the non operating issue or is there some other battery connection?
Jim

[Mbstrustee]

No picture attached. It was the single wire connected on top of the positive post on one of the 12 v batteries

[Jim Flower]

Thank you for that. Another place to look when stuff goes wrong. Jim

[RonJudi]

Had the same problem and found the JK wire connection is intermittent, Best to put new phone type connection phone cord Or JK to the first point which is the wiring which supplies the Voltage". Mine was the A/C Heat Pump'. I cleaned my connection on the roof and though it now works I suspect this is slightly corroded and will reoccur. A new thermostat did not help.

[Susansusan]

did you solve this problem. I have the same thing happening now.

[RonJudi]

I was able to go to the first Heat pump take off the cover and get to the phone type connectors, then exercise them after spraying electronic spray from Walmart. I had to do this several times but problem went away for a length of time. I sold that coach. My Guess is that you have corroded connectors as well. These J K connectors were designed with gold type alloys and I suspect compromised by manufacturers. Good news is though time consuming you should be able to get it going again. The 12 Volts from the coach comes from the A/C s feeding the thermostat and dark display indicates a faulty connection.