Dometic A/C compressor runs constantly

[smiller]

On my Dometic A/C the compressor has started to run all the time, meaning whenever power is applied to the unit (and regardless of thermostat position.) Fan operation is normal, it's just that when the set point is reached the fan shuts off but the compressor does not. I have tried disconnecting the 'Cool' wire in the thermostat but it makes no difference. I guess that isolates the problem away from the thermostat and to the relay control board in the main A/C unit?

[smiller]

Well nevermind, that one was easy. I pulled the relay board and checked the compressor control relay, contacts showed continuity even when powered off... until I tapped on it with a screwdriver . Working now but not gonna trust it of course, will get a new board on order.

[datatraveller]

I read the post by smiller about the a/c that wouldn't shut off, and is caused by a "stuck' relay contact. I have the exact same problem and would like to know how to identify the compressor relay. There are 3 black boxes that i see that could all be a compressor relay, but I'm not sure which one it is.Also where is a good reputable place to buy this control board? Any help would be greatly appreciated.Thanks,

Cam

[smiller]

It's the largest of the relays, near the center of the board, with external terminal connections on the top. Just about every online RV parts supplier has the board in stock, either grab the part number off of your board or look it up in the Dometic parts manual for your unit (available at the Dometic web site.) It will probably be 3106996.022 but check to be sure. They usually go for around $50.

[datatraveller]

You are absolutely correct, it is a 3106996-002. Is there any way to open the relay and possibly clean up the relay contact? Thanks very much for the quick reply, it's a relief to know it's not something much more expensive, and the repair procedure is simple as well.Appreciate the advice.

Thanks smiller.

[smiller]

Originally Posted by datatraveller

Is there any way to open the relay and possibly clean up the relay contact?

There might be and I considered that, but I didn't want to chance it because if the relay failed again while I was out of the unit then the compressor would be stuck on with no fan to cool the condenser, and I was concerned that might damage the compressor. Since loss of the compressor essentially means a new A/C with these units then... that would be bad. I just didn't want that thought sitting in my mind every time I was out.

[datatraveller]

Good point,I'll check for a new control board seeing how the difference in price between the control board and a new a/c unit is quite a bit more costly.Cheaper to do it right the first time. Thanks very much.

Cam