Community Forums

lc12 · 06-14-2010, 01:54 PM

Last weekend my wife turned the a/c off before using the microwave. When she did we heard a loud "thump" from the roof top a/c. A sound we had not heard before and it definitely got our attention. Sounded like something slamming shut. Since we were leaving we did not think much about it.
Well, this weekend we arrived late on Friday night and it was HOT inside the camper. First thing was to turn on the a/c.
While I was unloading the truck my wife said the a/c was not blowing any cool air!
The fan was working but I am guessing the compressor was not. I checked all of the fuses and they were OK, and the voltage was 113 volts.
So now I am assuming that the compressor is "stuck". Can they get a vapor lock? The a/c worked perfectly prior to the "shut-down" so I am thinking it is something that is not serious.
Worse thing is that the camper is on my farm and not really in an easy mode to travel so I would have to have someone come to the farm to work on it. Can a regular HVAC tech work on a RV air conditioner or will I have to find a RV technician to come out. I was thinking of trying one of the Supco SPP6 Super Compressor Boost Hard Start Capacitors and installing it myself.
The camper is a 1998 27ft. Starcraft 5th wheel with a Duo-Therm A/C rooftop unit.
Any ideas or suggestions would be greatly appreciated!

wa8yxm · 06-14-2010, 02:46 PM

Two posibilities

1: A/C is Toast

2: Screw loose.

Yup, many RVers have a few screws loose.. Some of the screws in my breaker box (Main power distrubution box) took as much as a turn and a half or more to tighten back up properly.. And after that my A/C's worked a WHOLE bunch better.

inspectorudy · 06-14-2010, 03:11 PM

See if Duotherm has a tech help line and call them.

GaryKD · 06-14-2010, 04:49 PM

Hi lc12,
Welcome to the iRV2 forum. Up on the roof, take off the A/C cover and determine if you are getting voltage to the two (I think) capacitors. Also, do the capacitors look okay or is there a burned look to them? All other things being okay (screw loose, etc) you may be on the right track by considering new capacitors. If the capacitor(s) are bad, replacement is a DIY project. Discharge the capacitors before unplugging them. I carry an extra set.

An HVAC tech should be able to work on the unit. When you call, ask to be sure. There is nothing unique about a roof A/C unit.

TXiceman · 06-15-2010, 05:23 AM

Do you have a Volt-Ohm meter (V-O-M)? They are not hard to use and the compressor is not hard to give a preliminary check.

Turn off the power and up on the roof, find the leads that feed the compressor/motor. Discharge any capacitors so you won't get a shock. Now check for continuity. First checl that you have continuity between the two motor leads and it is not an open circuit. Next check each motor lead for open or grounded to the compressor case. These should be open.

Next, you can use your V-O-M to make a quick check on the start capacitor. The instructions for you meter should outline this procedure.

Make sure you have at least 108 volts at the unit when the unit is operating.

Any decent A/C technician should be able to check the unit to see if it is OK or not. At the cost of repairing or replacing a unit, I would not spend more than $200.00 to repair a 12 year old unit.

Let us know how you come out.

Ken

lc12 · 06-15-2010, 06:09 AM

Thanks to all for your quick replies!
I did not think about the possibility of "loose screws". I am surprised my wife did not remind me of it!!!

It does not appear to be to tough to replace the capacitors. Bad thing is that I did not write down the S/N or Mod. #'s when I was at the farm so it looks like another two hour drive to get that info so that I can get the correct capacitors.
Do any of you know if the Supco's are an "assist" to the factory capacitors or would they be a REPLACEMENT for the originals?
Looks like Amazon.com has the best price on those.
I am sure that I have to be "model specific" in ordering the capacitors or are they pretty much generic when it comes to Duo-Therms?
Thanks again for the help, and have a good day!

Ray,IN · 06-15-2010, 08:03 PM

Ken alluded to a very important point. Minimum safe operating voltage is 120VAC + / - 10%. This calculates to a minimum of 108VAC and a maximum of 132VAC. Outside those parameters you slowly destroy your compressor(any inductive) motor. It's called "bruising"; kinda like your wife hitting you on the shoulder once an hour. The first few times it doesn't hurt much, but after 3-4 days you shoulder is severely bruised and will not work. Sorry for the bad analogy, hope it relates.

This is normally the result of using undersized extension cords, or trying to power too many electrics in your RV simultaneously.

Luv2go · 06-15-2010, 09:24 PM

Quote:

Originally Posted by lc12

Do any of you know if the Supco's are an "assist" to the factory capacitors or would they be a REPLACEMENT for the originals?

A/C compressors always have at least one cap, the "Run" cap. Most also have a "Start" or "Hard Start" cap that gets connected only when the motor is starting (using either a relay or a NTC thermistor). The Supco is a replacement for the "Start" cap and relay or NTC thermistor.

Quote:

I am sure that I have to be "model specific" in ordering the capacitors or are they pretty much generic when it comes to Duo-Therms?

Yes the caps are model-specific, although you could probably get away with one that is much larger or smaller in uF rating than the original. You should always replace with an equal or greater voltage rating (VAC). Also these should be specifically motor start/run caps, other AC caps may not work well in this application.

You've gotten a lot of good troubleshooting tips from Ken, here's my experience FWIW:

When I had this problem (1994 Coleman Mach), I actually had a bad "Hard Start" Relay, which turned out to be pretty specialized, had something like a 288VAC coil, not something you can find on most suppliers shelves. I could have used a Supco, replacing both the cap and the relay, but I ended up buying a hard start relay from the RV store, and the caps from an electronics supplier (much cheaper). To do this copy the brand and part numbers from the caps themselves and see if you can find them at Allied Electronics or Newark Electronics.

Note, if you have two caps and one is going bad I'd replace the other also just to be safe, plus the relay if there is one, as it will wear out. NTC's generally do not wear out so you should not need to replace it, if you have one.

Good luck!
Stewart