RV roof A/C trouble shooting:
 

I am recommissioning my old 1982 Airstream RV and the rooftop A/C units are not working. When I bought it in 2020, one of the two worked but now neither goes on. It seems to me that I've read previous threads here about home A/C units where some simple component caused the compressor not to fire up, I'm hoping to benefit from knowledge here and not have to bring it somewhere...any advice on what to check or look at? I know next to nothing but I do have a multimeter and test light.

Major thanks in advance. It's supposed to hit 103 here today, first real heat wave of the summer. I want to take the RV to the beach! :cool:

Low on freon would be my first guess.
Second would be electronics.

Is that a 120v AC unit? Motor start capacitor or relay? The low on freon as Arizona mentioned.

What brand are the units? Assume you are hooked up to 30amp service and have power (checked circuit breakers etc) to the thermostat and the unit itself? Does the fan come on when just in fan only mode?

In a home AC unit typically the compressor motors use a capacitor start system. When they fail to run it can often be as simple as replacing the capacitor but I am not sure about your particular AC units.

My 2004 coach AC units sometimes take several minutes before they start up after turning them on at the digital thermostat wall mounted controller. IAt first I thought they were not working but they always start eventually.

Went through this when my brother visited in his RV and A/C quit on his. We went on line and did some basic research and ended up changing out his start capacitors that were originals. Also some wiring connections were a bit corroded and or loose. Believe we found the caps at auto parts store or maybe the local RV dealer,not sure. There are quite a few educational U-tube videos out there as well. Good luck!

Here's a couple sites that might get you headed in the right direction:
https://evapolar.com/blog/air-conditioner-does-not-keep-rv-cool/
https://www.fulltimefamilies.com/rv-ac-repair-guide/

Are the AC units the ones from the 80s or more recent dometic style units? "neither goes on" is also kind of vague, much like "car won't start." To stick with "car won't start" analogy is this
1) I turn the key and nothing whatsoever happens (maybe no power/fuse/thermostat wiring issue)
2) I turn the key and the lights on the dash light up but nothing else happens (maybe thermostat or capacitor issue)
3) I turn the key and I hear a click click click but nothing else (maybe a compressor seize issue)
4) I turn the key, the engine starts but dies (OK analogy dies here but you get it, running but not cold is maybe R134 issue)
etc etc

Yes, 120v units. I’ll remove the covers and take pictures so that you guys can help me identify the parts.

See if the evap coil and condenser fans spin freely and don't have stuff in them.
Sometimes there is a condenser high pressure cut out switch that opens and can be reset.
Check the motor contactors and the start capacitors.

They each have dial controls and they do not turn on. No fan, nada.

As noted, most A/C issues where the compressor does not run is the start/run capacitor...although a bad compressor or the compressor thermal cutout switch (in the compressor will keep it from starting). In my experience, a bad compressor typically pops breakers as it shorts to ground...so more obvious.

The caps (usually one for the compressor and one for the fan) are easy to test and often you can tell just by inspection (bulges or leaking). If the fan doesn't run, the compressor may cut out (thermal cutout). It does not reset until the compressor is cool.

You likely have a 120v contactor of some sort. It is just a big relay. When on, you should have 120V on the input and the output (as measured across the input/output leads). I start there with an A/C unit where nothing works. The contactor in most home units (they are 220) allow you to manually close the contacts which should turn on the fan and compressor while you hold it.

Check for mice.

The primary things that goes wrong on Air Conditioning units is loss of freon followed by a dead capacitor and then the motor contactor. I keep spares for those fixes, because the AC always goes out on July 4th or Labor Day weekend...

A compressor that is low on freon will usually run (fan and compressor), but not cool the air.

On a similar note, my boats freezer quit a few weeks ago. I was dreading it because it meant, as a minimum, emptying out a storage locker and contorting into a cramped space to diagnose the fridge unit. And worst case, $1300 for a new unit, plus installation.

But there a lots of good diagnosis checklists on line. For an older unit especially, because there has probably been lots of DIY repairs posted over the years. Look up the model and do a search. You may be surprised what you find.

In my case I dodged a bullet. First item: Verify power to the unit. When I got to the unit I could see that one of the power wires was pulled off of its connector. Reconnected and off she went. I was so happy. Boats rarely give a freeby.

If you can't run the fans in FAN mode, I'd start with checking for power to the units, first.

These units are usually simple, shoot some detailed photos and we can show you what to poke and prod. The circuit board, or what passes for one in these units, might be accessible from inside the RV, where the air duct is.

Thanks, guys. It’s too hot to climb up on the roof of it today, (I’m at the beach), but I shot a couple of the interior part of it before I left. I might be able to climb on it tonight.

http://forums.pelicanparts.com/uploa...1725581765.jpg
http://forums.pelicanparts.com/uploa...1725581765.jpg
http://forums.pelicanparts.com/uploa...1725581765.jpg

I would start by seeing if you got power to the board and then going from there.

There's the problem. You are running it in the "OFF" mode.

Sheet, it's a 1982 unit? just replace. simple.

Not if they are still good. One of them was working great when I bought it in 2020 and the other did not turn on. Now, after sitting for 4 more years, neither go on. If they need to be replaced, I will replace them but first I need to determine what's up. :cool: