AC screwing up

Devilishjim · August 1, 2017

Hi my Dometic duo-therm 15K is having issues. The compressor kicked on all by itself but not the fan. I shut breaker off and turned back on and it was fine but somwhere along the line it tried again and dumped my breaker., This was with thermostat in off position.

So I set thermostat so it would come on and fan and compressor ran and cooled things right down, but then I moved thermostat so that it would shut down / The fan shut off but compressor kept running until I shut off the breaker.

My thinking is this unit is12 yrs old and my thoughts are a new thermostat. Its a duotherm that controls AC and central heat. What are your thoughts on this and if the thermostat can I replace it with a digital or should I go with OEM or pull it off the wall and blow some dust out of it. Sure glad it only gets to 85 here !

Wrknrvr · August 1, 2017

I think it is the PC board for the ac. The thermostat sends signal to the board for the unit to come on.

the board controls the fan spreads and when the compressor comes on.

Just my thoughts,. Vern

Biker56 · August 1, 2017

Open the thermostat up and spray inside with electrical cleaner.
Especially the temp adjustment slide if it is not digital.

And you can replace it with a digital one if that doesn't work.

That worked on mine to make the thermostat last several more months.

Kirk W · August 1, 2017

My reaction is the same as Vern's. The thermostat only sends a signal to indicate that the temperature is either above or below the set point. The controls for starting the blower and compressor are part of the air conditioner. You probably have the old style of Dometic thermostat.

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They are quite available and cost a bit more than $30 and are easy to replace so you could try it without spending too much, but I'll be surprised if it helps. If it were me, I'd visit Bryant RV website and download a copy of the manuals for both your thermostat and your air conditioner and study those before I went too far. I'm thinking that this manual will cover what you need and the trouble shooting for the system you probably have starts on page 102.

Devilishjim · August 1, 2017

I see in parts a dinosaur and relay board are these inside up on top ? gonna try Bikers fix with contact cleaner to day and if that works will probably order a new thermostat... I had the problem before where nothing would work and between working slider and wiggling fuses it started working again. My lids on ACs are getting brittle too guess its time to replace those two, wonder what the odds are of getting those shipped to me without getting broke ? I should be able to test the thermostat with my Fluke meter right ?

I can get by with bedroom AC up here but I prefer the other one when I crawl in bed...lots quieter

Ranger Smith · August 1, 2017

When mine did that it was the control board in the ac unit

Kirk W · August 1, 2017

6 hours ago, Devilishjim said:

I should be able to test the thermostat with my Fluke meter right ?

For both voltage and resistance readings, the answer is yes but you need to use the trouble shooting guide that I mentioned from Bryant RV in order to know what to look for. It just depends on what control center your RV has, how much of it you will be able to check.

Devilishjim · August 2, 2017

3 hours ago, Kirk Wood said:

For both voltage and resistance readings, the answer is yes but you need to use the trouble shooting guide that I mentioned from Bryant RV in order to know what to look for. It just depends on what control center your RV has, how much of it you will be able to check.

Where do I find the PC board above the face plate or under the cover on the roof and as I recall serial # is under face plate. Now if I was a Dr I could fix this with the motor running :unsure: :blink: . I need to order parts w/o shutting AC off, as the sun goes down I can switch to bedroom AC The living room I have to use breaker to shut down. Anybody have a good source for a replacement PC board ?

Pat & Pete · August 2, 2017

2 hours ago, Devilishjim said:

Where do I find the PC board above the face plate or under the cover on the roof and as I recall serial # is under face plate. Now if I was a Dr I could fix this with the motor running. I need to order parts w/o shutting AC off, as the sun goes down I can switch to bedroom AC The living room I have to use breaker to shut down. Anybody have a good source for a replacement PC board ?

Just Google ' Dometic duo-therm AC circuit board' . Take your choice .

When our AC ( Duo Therm ) went haywire , I pulled the circuit board from inside the 'control' box ( located just above the interior shroud ) . I simply replaced the relay on that board . Cost me less than 10 bucks , as opposed to $90+ for the complete board , which looked good otherwise . Of course , the replacement requires a little soldering .

Here's the relay I replaced the original one with :

http://www.ebay.com/itm/Potter-Brumfield-T9AS1D22-12-30A-relay-240VAC-30-amps-240-volts-SPST-NO-/121800223629?epid=667260745&hash=item1c5bdbeb8d:g:T9AAAOSwjDZYhQKg

BTW , our AC works just fine ever since .

Kirk W · August 2, 2017

11 hours ago, Devilishjim said:

Where do I find the PC board above the face plate or under the cover on the roof and as I recall serial # is under face plate.

If it is like the units that I have worked on, after you remove the inside cover you will see a metal box that has a removable cover and the electronic controls are inside of that. Remove the cover and you should be able to see what you are looking for.

Pete is correct that is it probably only 1 of the relays so if you are comfortable doing that, you could replace only the bad relay. If not, changing the entire circuit board will cost less than a service call from a tech would cost.

Devilishjim · August 2, 2017

6 minutes ago, Kirk Wood said:

If it is like the units that I have worked on, after you remove the inside cover you will see a metal box that has a removable cover and the electronic controls are inside of that. Remove the cover and you should be able to see what you are looking for.

Pete is correct that is it probably only 1 of the relays so if you are comfortable doing that, you could replace only the bad relay. If not, changing the entire circuit board will cost less than a service call from a tech would cost.

Yes the whole board sounds good to me and then if I feel like tinkering with the old one I can sell it to Pete n Pat when his soldering job blows Got a CPR class this morning and then campers so maybe tomorrow be able to look at it. I must be really slowing down this 5hr per day seems to stretch into a very super long day !

Pat & Pete · August 2, 2017

1 hour ago, Devilishjim said:

Yes the whole board sounds good to me and then if I feel like tinkering with the old one I can sell it to Pete n Pat when his soldering job blows Got a CPR class this morning and then campers so maybe tomorrow be able to look at it. I must be really slowing down this 5hr per day seems to stretch into a very super long day !

Ha . I'll let you 'give' me your old board , so I can replace what needs . Then I'll 'sell' it back to you as a spare ..

My soldering will not blow . Too many times soldering components on computer boards and such , using silver solder has taught me well enough .

But yeah , unplugging the old board and plugging the new one in is maybe 5 minutes easier .

And , there's only a single relay on that board , so there's no chance of confusion . Am I giving away too many secrets ? LOL

Devilishjim · October 25, 2017

I installed a new board and my ac compressor still wants to run AC friend came and looked at it and seems I got a defective board. Is it possible I switch the two wires going to relay and would that cause the problem ? Can I switch those two wires too see if that would rectify my problem ? Growing old isnt easy !