AC heat...running together!

The AC compressor is NOT on. Your AC FAN is ON. READ the directions for the wall tstat. You MUST set the FAN on the wall tstat to AUTO. If you do NOT, then the roof AC Fan will come on in either LO of Hi depending on what the wall tstat is set at. Dometic does this to help circulate the furnace air in the RV. Doug

Are you positive that you don't have an AC with a Heat Pump? Good option for saving propane and I know that when I first turn it on, both will run for a while depending on the outside temp.

notruffinit....the AC is blowing COLD air....

Had that happen a few times with my Cougar. My Cougar also had a remote that I had difficulty with, so I replaced the thermostat and threw the remote away (in recycling bin). No issues since. Occasionally, the old way is better and simpler to use, at least for an old f$$t.

gon2dadawgs wrote:
notruffinit....the AC is blowing COLD air....

Have you checked the Fan setting like I asked?????? Cold air is relative. Are you positive it is NOT just blowing the cool air in the RV??? What I have stated is a VERY common problem on the new Dometic wall tstats as customers do not read the directions and the delivery person never states this. Doug

johnrbd wrote:
Had that happen a few times with my Cougar. My Cougar also had a remote that I had difficulty with, so I replaced the thermostat and threw the remote away (in recycling bin). No issues since. Occasionally, the old way is better and simpler to use, at least for an old f$$t.

The poster does not have a remote, he has a wall tstat. Doug

gon2dadawgs,

My Dometic AC just did the same thing. My T-stat is not digital, however.

Doug, I always appreciate your experience & advice and took note of your post above. Have you ever come across a condition where the AC ran regardless of the thermostat settings?

I went out to exercise the generator using the heat strips. When I went to shut down the heat strips and walked toward the front of the vehicle, I could hear my front AC compressor running. There is no doubt about it, the compressor IS running, I can hear the hum and it's blowing cold air. This is with the thermostat in the OFF position. The only way to shut it off was with the breaker. The rear AC is working normally. This happened with the generator and again when I switched to shore power.

I did have one episode in the Fall where I thought the AC came on with the switch in the OFF position, but when I moved the switch to "HEAT" and back to off, the AC shut down & stayed off. But no joy today. The compressor is ON and the thermostat doesn't seem to be able to shut it off regardless of temp/HEAT/AC settings or the Fan/ON/OFF/Auto settings. Nothing on the thermostat control seemed to be able to shut down the front AC.

We have a cold snap heading our way, so I won't be working on it till it warms up, but I'm guessing the Dometic DuoTherm thermostat is shot. I killed the breaker and put the RV back to bed for now. When it warms up, I'll take the T-stat down and see if it's repairable in any way.

I just hope the AC hasn't been running for the past month without my knowing it. I better check the electric bill! LOL

~Rick

Rick Jay wrote:
gon2dadawgs,

My Dometic AC just did the same thing. My T-stat is not digital, however.

Doug, I always appreciate your experience & advice and took note of your post above. Have you ever come across a condition where the AC ran regardless of the thermostat settings?

I went out to exercise the generator using the heat strips. When I went to shut down the heat strips and walked toward the front of the vehicle, I could hear my front AC compressor running. There is no doubt about it, the compressor IS running, I can hear the hum and it's blowing cold air. This is with the thermostat in the OFF position. The only way to shut it off was with the breaker. The rear AC is working normally. This happened with the generator and again when I switched to shore power.

I did have one episode in the Fall where I thought the AC came on with the switch in the OFF position, but when I moved the switch to "HEAT" and back to off, the AC shut down & stayed off. But no joy today. The compressor is ON and the thermostat doesn't seem to be able to shut it off regardless of temp/HEAT/AC settings or the Fan/ON/OFF/Auto settings. Nothing on the thermostat control seemed to be able to shut down the front AC.

We have a cold snap heading our way, so I won't be working on it till it warms up, but I'm guessing the Dometic DuoTherm thermostat is shot. I killed the breaker and put the RV back to bed for now. When it warms up, I'll take the T-stat down and see if it's repairable in any way.

I just hope the AC hasn't been running for the past month without my knowing it. I better check the electric bill! LOL

~Rick

IF the wall tstat is OFF and the compressor runs, then on YOUR system the compressor relay on the upper control board is stuck. You need to replace the upper control board. It may unstick by itself, but the fact it stuck once means it will do it again. Doug

Hi Doug,

Thanks for the advice. When it warms up I'll go out and take a look at the board. I did find a Dometic AC Service Manual pdf on line and it seems to have some helpful information. As near as I can tell, everything else on the AC/Heat system works fine, so I might just try replacing the relay instead of the entire board. I had good luck going that route replacing a bad relay on our slide controller a few years back.

Thanks again for your prompt advice.

~Rick

Micheal

I know this is an old post but if you haven't solved your problem yet here is one solution;

With regards to your thermostat, I had a salesman/manager show me how to reset the system if both AC and furnace fans came on together.

Cycle thermostat to off (no display), press and hold the + button first and without releasing it press the on/off button and hold. After a few seconds the display will indicate --. Release both buttons and then press the on/off button to turn off the system. In the thermostat manual this is called the 'System Initialization' which should have been performed by the installer.

Hope this helps.