AC died, compressor won't start

[timmyjane]

I have a Coleman unit that seems to be giving problems lately.  At the end of last summer I installed all new caps and a new blower motor. 
This past weekend the compressor would not kick on.  The fan runs as it should.  The unit is manually controlled and is AC only.  I removed the lower ceiling assembly to check for loose wires because I had previously removed the grill for unrelated work to the RV. 
On inspection everything was connected and tight.  Looking at the thermostat it appeared to only have 2 wires.  Seems maybe red going in and yellow coming out.  I thought that maybe the thermostat worked as a relay and may not be working correctly so I connected the out wire to the in.  No go, compressor did not kick on. 
We just got home today and it was raining so I haven't gone on the roof to inspect yet.  Does anyone have any thoughts on how to try and manually kick on the compressor to check for function and try and diagnose the issue?  The run cap may have gone bad but it seems unlikely since its only about 6 months old and we are not fulltimers. 

 

[Boonieman]

Actually, the thermostat sends a low voltage signal to a start relay. If you have a voltage tester you could make sure that when the thermostat "makes", (tries to start the compressor)it's sending voltage to the relay. Not being familiar with your system, hard to say what that voltage is, but most likely 12v DC. You should have 12 volts coming to one side of the thermostat, and when the thermostat "makes", (trying to turn on the AC) you should have 12 volts heading toward the start relay. If you have voltage going out, I would assume the thermostat to be good, then look at the start relay. There are plenty of other ways to force a compressor motor to try to run, and I apologize, but I sure wouldn't give out that kind of advice on a forum because it can be dangerous or damaging to your equipment, even if done properly. Hope you get it going!

 

[rvpuller]

You will need a meter and basic skills on how to use it, becase the electric box is so compact the easiest way to see if the compressor is getting power is to remove the terminal cover and with everything on check for voltage between the C and R leads, if you have no power there is a overload relay in series with the C terminal, check for power on the other side of the overload relay. If you have power coming into the overload it's either bad or tripped, if it tripped it will reset in less than a minute. From there if you have no power check backwards all the way to the control board, there is a separate relay mounted on it for the compressor.

Denny

 

[timmyjane]

Thanks for the tips. It been a busy few weeks so I haven't delt with the AC yet. Went camping last weekend and only used the back unit.  I follow this advice and see what I come up with. Anyone have a wiring diagram that shows the complete unit?  Relays and all?  I've got to get on the ball and fix it or replace it. Unsure yet what's the best path.  I think the unit is 12 years old so it may be best just to replace it.  Could be becoming a time and money pit.

 

[Natetheskate]

I had a similar issue recently, and it turned out that squirrels had made a den in my AC shroud, and had chewed through the wiring.