Both roof top AC units not working.

GA

garyb1st

Senior Member
Joined
Dec 31, 2010
Posts
5,292
On our last trip one of our front Coleman AC unit stopped working. I could hear it start up but the compressor would not engage. The rear AC worked fine. After taking it to the service guy, I was told the compressor failed and I needed a new AC. $2200 for the unit installed. That was Wednesday.

Not totally happy with the service facility, I went out today and tried to start it. Nothing. Not even the initial start up like before. Then I tried to start the rear unit. I could hear it turn on but the compressor would not engage. Just like the front unit before I took it in for service.
I was able to run the fan on the rear unit without problem. But when I switched the thermostat to cool the fan eventually stopped working.

I've read it could be a capacitor or possibly a relay. Tried to find the relay in the front engine compartment fuse box and nothing there. Not sure where else to look.

I also read it could be a simple thing like a tripped breaker. Switched them both off, waited a few minutes and switched them back on. I also checked the fuses on the generator. They appeared to be fine. Switched them off and back on. Nothing.

One thing that puzzles me is a loud clicking sound when I waiting for the unit to start. Never heard that before.

Can anyone suggest another way to check the compressor.
 
You didn't give the age of your unit but odds are high it's the start and run capacitors. They're inexpensive and easy to change. It could still be a bad compressor, fan, or both. You can try spinning the fan by hand to see if it's binding. I wouldn't look at anything else until the caps are replaced. The clicking could be the thermal cutout activating due to a stalled fan or compressor. With 2 A/C units you might have a system that splits them between a 30A and 50A supply, but not both when on 30A. I would treat that as a separate problem. I would at least troubleshoot to a functional level as it appears your repair resource isn't as much about troubleshooting as parts changers.

Mark B.
Albuquerque, NM
 
Found a young man who does RV AC work. Hopefully he'll be able to at least confirm whether or not the units can be repaired. I'm hoping it's the capacitors and not the compressors. But at least I'll have another opinion. The units are original and the motorhome is a 2005 so they've been used.
 
If compressor is bad, I would not attempt repairs, replace the unit.
There is nothing special about capacitors, just buy one with the same numbers on the side.
Any electrical supply store will have them. Most are less than $15 ea. I had the time so ordered from Amazon.
How to determine if a capacitor is bad:
 
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Funny thing about air conditioners. If the ambient temp is lower than the temp setting on the thermostat, they probably wont' come one.:oops: Hopefully that was all that was wrong on the back unit. It did start today when the ambient temps were in the low 70's. Didn't get real cold but it felt a bit cooler than the ambient temp.

The front is back to behaving as before. When I turn it on, it takes a while but the amps eventually get to about 9 or 10. I'm pretty sure that's not enough for the compressor to kick in. Hopefully something simple like a Capacitor or other minor electrical issue. At least we should be able to travel with one if we can't sort out the other unit.
 
What are you measuring that current with? A clamp on amp meter I'm guessing? And where are you measuring it? If that is just the AC unit circuit that current is too high for the compressor to not be running but not high enough if it is. I think mine pull between 15 and 18 amps running. Of course the end rush current is much higher. You can't do much troubleshooting on these units without being on the roof with them. Your statement about the current not getting high enough for the compressor to kick in doesn't make sense to me. Current/amps are a result of the compressor running not a requirement for it to run. I assume you had the guy you found look at the units. What was his diagnosis?
 
Check out Houghton by rec-pro. They have their own handheld thermostat. Super quiet
 
Our motorhome has a meter that measures amps being used by the appliances. Normally when starting the large AC the amps are about 11 before the compressor kicks in. After the compressor kicks in, the amps bump up to around 18. The smaller of the two units is similar with lower starting and running amps. Combined amperage shown when both units are working is usually under 30. How accurate that is I can't say. Our coach has 50 amp service. When we're at parks that only have 30 amps, we watch the amp meter carefully to keep total draw under 30. Usually we'll be at 27 give or take.

From what I've read, the compressor has a higher starting amperage. (I suspect that's where the soft start device comes in) I've also read that if the compressor is bad, the fan will still run. Our does not run. So a more general electrical rather than compressor specific issue. Hopefully we'll know by tomorrow.

The man that was coming to check things out was unable to make it last Monday. I'm hoping he can tomorrow. If not, I've got another service company I can call. But I suspect getting in before we'd like to move may not be possible. If it warms enough today I'll test the rear AC again. If it works we're leaving weather or not the front, more powerful unit, works. Only downside will be a couple of warm nights during a heat wave. Hopefully we'll be back before that happens.
 
garyb1st said:
Didn't get real cold but it felt a bit cooler than the ambient temp.
Click to expand...
The best way to check the operation of an air conditioner is to accurately read the air temperature into the unit and also out of the unit when running. That change should be between 18° & 24° F. Any more and the unit will probably freeze up and less means less than designed efficiency.
garyb1st said:
From what I've read, the compressor has a higher starting amperage. (I suspect that's where the soft start device comes in) I've also read that if the compressor is bad, the fan will still run. Our does not run.
Click to expand...
Compressors typically have a starting current that is several times that of the run current and that is the reason that they have a start capacitor. Capacitors actually store amps and in effect boost the start for part of a second. Without the capacitor the supply isn't enough to get it started but that current drops off as the motor begins to turn. You are also correct about what the soft start device does. It is true that in most (if not all) RV air conditioners, the blower will run even if the compressor does not. In normal operation the blower starts first to get air moving through the cooling coils before the compressor begins, but only a second or two before.
garyb1st said:
Our motorhome has a meter that measures amps being used by the appliances.
Click to expand...
That reading would be all power being used by everything in the RV so should be somewhat higher than what the air conditioner is using. Just how accurate it may be is anyone's guess. The only way to be sure is by using a good, clamp-on ammeter.
garyb1st said:
Tried to find the relay in the front engine compartment fuse box and nothing there.
Click to expand...
The capacitors and relays are inside of the air conditioners, usually accessed by going on the roof and removing the cover.
 
Those old Coleman coolers are darn near bullet proof. Simple to fix too. Fan motors are around $100 on Amazon. I replaced all three capacitors in one of mine for about $70. The only thing that isn't easy to replace is the compressor.

Do you trust the RV tech who said you need a new AC unit? (I admit to having trust issues with RV techs)
 
8Muddypaws said:
Do you trust the RV tech who said you need a new AC unit? (I admit to having trust issues with RV techs)
Click to expand...
No, I don't trust the guy. Current guy took over shop about 3 years ago. Previous guy was high priced but at least he was honest. This guy strikes me as dishonest and just as high priced.
 
garyb1st said:
No, I don't trust the guy. Current guy took over shop about 3 years ago. Previous guy was high priced but at least he was honest. This guy strikes me as dishonest and just as high priced.
Click to expand...
It's unlikely anyone is going to start replacing parts on a 20 year old rooftop a/c with a struggling compressor. Residential guys will throw a hardstart capacitor into a unit to extend the life of an old compressor. Something like that might work on your rooftop unit.
 
Bad capacitors will make a compressor struggle.

It took me less than an hour to replace mine and also clean the A and B coils. $70 for parts, $20 for fin foam, and an hour on the roof saved me thousands.

And nobody had to rent a fork lift to get the heavy booger on the roof.

Oh, and I got bragging rights too! ;)
 
Update and correction. Correction first. Only one AC was not working. Other AC that local Los Angeles repair shop said had a bad compressor, couldn't be fixed and would cost $2,200 to replace, apparently didn't have a bad compressor.

Yesterday, we were at an RV park in Alpine TX. Local RV repair guy comes out to look at the AC. Finds several pieces of foam that were lodged in the unit. Takes them out and the AC starts and runs like always. Not sure where they were and not sure why I didn't see them when I pulled the cover off the unit a week ago and didn't see them. But it's working. Always thought the guy in L.A. was not totally honest. Now I'm sure. He'll be getting a review he won't like.
 
With shore power disconnected and genny off, open the power center and carefully inspect and re-tighten every connection on the breakers, ground, and neutral bars. If you have an auto xfer switch, find it and open it and check for burned and loose connections. Use a screwdriver, and physically attempt to tighten every connection, don't just look at it and assume it's tight. This should be done every year or two.

Charles
 
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