Air Cond will not work

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Theo2

New member
Joined
Jul 10, 2020
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4
Hello All, Newbe here. As the title states my air cond will not run, had it going once and shut it down but it will not come back on. Its a older Mallard 5th wheel camper, the air cond. is a DuoTherm model 58915.302 with a Dometic 3109228.001 model thermostat. When it was running it worked good and throwing plenty of cold air, now i cant even get the thermostat to power up, could it be a bad thermostat? It has like a phone cord plugged into it and runs to top of air cond. Are these thermostats noted for going bad? Any trouble shooting tips would be very helpful. 
 
Welcome Theo2. It could be a bad thermostat, but have you checked the power source, and the RV's circuit breaker(s)? You didn't say what you're plugged in to (campground power pedestal, residential outlet, generator) but each will have it's own breaker and/or gfi. The RV will also have an AC breaker and likely a Main breaker. Are any other A/C appliances working?

Kev
 
Welcome to the forum. I?m by no means an expert but you?re going to Be asked if you have 12 volt DC power at the thermostat. Another thing have you checked to see if the 110 volt AC circuit breaker has tripped. It?s hard to tell sometimes just by looking at it . You have to shut it off then back on. The experts will chime in soon to help you.

Oops, Kev beat me
 
Plugged into home 20 amp circut. No breakers are tripped and the 12 volt fuse on top of the air cond. is good. It was running good one day then the next day no run, come to think of it i had to play with the thermostat some that first day to get it running. I just dont want to be changing parts not knowing for sure if that is the problem or not, i need to know how i can check for 12 volt at thermostat. The line running to the thermostat is like a telephone cord line with the jack plug going into the back of the thermostat
 
Have you tried tapping on the thermostat?

Have you tried removing the filter from the air conditioner and giving the Impeller a spin?  They sometimes won't start spinning.

 
Thermostats come in 3 types for this post and only two apply
First the one that does not apply is a straight mechanical T-Stat such as I use for my Furnace. It needs no power (You said it would not power up hence it does not apply)

The other two use either house 12 volt ... Usually from the Furnace  Or internal batteries.. or both.

My first susdpect ids dead internal battery
2nd is the Furnace ..  Now I only know one make (Atwood) there is a switch (Outside on top of the blower housing in my case) really a circuit breaker. make sure it is on.  also pull the control board, unplug, inspect (visually) be prepared to say OH ****! when you see the condition of the traces

ONE of the blue wires should show 12 volt to ground when you plug back in

Beyond that you may need to throw money at it.

NOTE: if the traces on the control board are corrorded away  Dinosaur boards is what I recommend.
 
You need to check the 12v power at the thermostat, not the fuse at the a/c.

Download a troubleshooting guide for your thermostat at https://www.manualslib.com/manual/1334900/Dometic-3109228-001.html

Yes, the Dometic Comfort Control thermostat seems less reliable than some of the simpler models, but I wouldn't leap to any conclusions based on such slim data. There are several possibilities besides a defective t-stat.
 
OK Gentlemen, I finally got to check for 12 volt at the T-Stat and have none, whats my next move? Where should this air cond. be getting 12 volt from for the thermostat? Would it be coming from the 12 volt aux. panel down by the breaker box or would the rooftop air cond have a transformer in it to step the 110 volt down to 12 volt?
 
The 110 volts is A/C....alternating current.

The 12 volts is D/C  direct current.

You get the 12 volts D/C direct current from your house batteries.

When you measured the voltage what setting did you use on the voltmeter...AC or DC?
 
T-Stat power normally comes from one of the BLUE wires on the Furnace controller.  The other one is the return to the furnace to fire it up in case you wonder.
On an Atwood furnace there is a switch atop the blower housing. this is actually a circuit breaker
Check there both terminals.  beyond that ... Good luck tracking the no power issue.
 
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