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Dometic ct thermost


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I have a problem with Ac on my 5th. I have a Dometic CT thermostat and everything on the control panel seems to function correctly(temp adjustment, switch from hear to air, fan speed etc). The ac will run fine when set to auto and will cycle from high to low and then off when it reaches set temp.
However it will not cycle back on when the air temp exceeds the set temp. I have to turn it to off then reset to ac. Then it will start back up runs to the set temp and then repeats the problem. I just put this new thermostat on last summer and it worked fine but last 2 trips this problem. 
any suggestions.

btw this is a 3 wire thermostat. 

Edited by etu
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I have experienced this same problem.  I never determined the cause but found resetting the thermostat seemed to fix the issue.  On mine, you press the mode button until it is off then press the mode and up buttons together until you see -- on the display.

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Yes that’s what mine is doing. I think I’ll reinstall my original thermostat which I replaced only because I wanted one with an illuminated panel for nighttime. Otherwise it worked fine. If I still have the problem after switching thermostat I assume it’s a bad connection on one of the 3 wires at the thermostat or at the unit. 
Is there anything else it could be ?

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Ok so I called Dometic ts and they said it sounds like the thermostat is bad. I just bought it last year but it’s past the 1 year warranty. Suggested I buy one online. If that doesn’t solve the problem they suggest replacing the circuit board on the AC unit. 
I’ll put my original thermostat back on and see what happens (it worked fine but did not have a back light). 
I’ll update what I find. 

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To truly check the output is to check the temp drop at the unit after it's been running for 20 minutes. Check temp at the return and at the output, there should be a 20 degree difference. Just my guess but you will find it's the ductwork causing your problem. An example would be 80 in 60 out, as the temp goes down in the RV the output temp will decrease. Sometimes the RV insulation is so bad that the temp will not come down.


Edited by D&J

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Update. Ac did not work any better when I changed thermostats. So got a mobile AC tech coming tomorrow. 

Update 10/3. First, our camper is a 2016 cougar 303rl (33’ long).  It has one 15k btu Dometic B59516 ac in the kitchen/ rear living area. 
Had the Refrigeration/HVAC mobile tech come today. Fins and coils are clean and the best we could get is 16-17 degree differential between return air and cold side. Went ahead and changed out the control kit including thermostat but didn’t make any difference.
He said the unit behaves as if it’s low on charge but the cost of 410 and installation of ports don’t justify the cost (~$500) that could go towards a new unit with 2 year warranty. 
We have a trip planned in 2 weeks in the north Ga mountains and cooler weather. I think I’ll wait until we get back from that trip to replace the AC. 

I guess if I go with Dometic all the lower(interior) components are plug and play. If I go with another brand I’d have to replace the lower unit as well. 
I’m leaning towards replacing the upper with the Dometic and do it myself but I’ll need to think about that and see some videos before I decide. 

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