Runaway Compressor

[Volunteer]

I have two Coleman rooftop units on my 1996 Discovery and a couple of times last Summer the front unit's compressor would keep running after I turned the unit off at the electronic control center. I would simply turn off the dedicated breaker for the front air conditioner and this would stop the compressor from continuing to run. Next day, everything would be back to normal after I kicked the breaker on.

But late in the Summer when the compressor kept running after I turned the air conditioner off, it wouldn't stop when I turned off the breaker. The only way I could stop the compressor from running was to reach up and unplug the white square plug connecting the air conditioner's on-board electrical center with the Discovery's air conditioner control harness.

I replaced the compressor run capacitor, thinking maybe this was the culprit, but the compressor still runs even though the breaker is in the off position.

Any ideas on what might be giving me this runaway compressor???

[CaptBill]

If you have an air-conditioner that continues to run when you turn off it's breaker, I want it!

You need to check your breakers' labeling. If you turned off the breaker to *that* A/C unit, it would shut down. Turn off other breakers until you find which one is for that unit. If you have 2 roof airs, they are probably on their own, individual breakers.

The other problem (A/C not shutting off when T-stat is satisfied), could be a bad T-stat or a sticking relay in the A/C. Capacitors would have to do with the unit failing to start/run.

[Volunteer]

I knew I should have gone into more detail. My fault.

There was a time last year when killing the breaker (it's 30-amp and just for this front air conditioner) would stop the compressor from running on.

Now, the fan (blower) stops running when the thermostat's setting is satisfied but the compressor just keeps on running. I've killed every breaker in the house and the compressor just keeps on running.

The only thing I've found so far that will stop the compressor from running is pulling my main electrical plug out of the RV park's electrical supply box or pulling the white square plug off the air conditioner's circuit board.

I agree. It doesn't sound logical that there is power bypassing the 30-amp breaker to keep the compressor running. But there is and that is the problem I'm trying to solve.

I was just hoping this had happened to another owner of a 12 or 13-year old Fleetwood motor home.

[aa6vh]

If your compress really does not shut down when you flip its breaker, then:

1. You still haven't found the right breaker.

or

2. You have a really dangerous condition here. Having that much load on an unprotected circuit can lead to very bad things happening. If this is the case, I would suggest you get the trailer to a qualified electrician as soon as you can to rectify this. In the meantime, do not run the air conditioner.

[Luv2go]

I agree with the other posters on the breaker thing, one of the breakers in your box should shut down the unit without having to resort to pulling either plug. It's possible the breaker has gone bad, but not likely as they are designed to be failsafe. The fact that the breaker used to work and now it doesn't leads me to believe that that may be the case, however.

One thing that would cause the unit to shut down even if you flipped the wrong breaker is an Intellitec EMS system. When you flip either of the two breakers that the Intellitec senses to see if you are on 50 or 30A, it will shut off all controlled loads, which usually include the A/C's until it finishes figuring out what happened to the line voltage (i.e. the display segment stops going round and round)

As far as the compressor running on after the fan turns off, I had this happen to me on a 1994 Coleman Mach unit. The only way I could turn off the compressor was turning off the breaker. I found one of the relays on the control panel had stuck closed. Replacing the relays fixed it. I found the relays at Digikey by matching part numbers. If you don't want to tackle the soldering, etc, you can replace the whole board, unfortunately, I don't know where to start looking for one except for calling the mfr.

But I'd definitely get the breaker thing fixed first, it sounds dangerous! You can try replacing the breaker, most RV boxes use BR or BRD type breakers (Cutler Hammer/Westinghouse/Bryant), you can remove the breaker and match it up at your favorite home improvement store.

A word of caution, as aa6vh said, if you are not experienced with working on things electrical, let an expert handle it.

Good luck!
Stewart

[RV Wizard]

Most likely the breaker has also now gone south. Turn the fan on and retry breaker. If the fan continue to run, then the breaker is bad. Circuit breakers are not designed to be used as switches over and over for long periods of time. The compressor relay on the control board is not opening (welded) allowing the compressor to continue to run. You should check the unit closely before dropping much money on repairs as you could have other issue to cause the points to weld together like high compressor amperage.

[Luv2go]

RV Wizard, you have a good point. I remember now that I also found a stuck hard start relay that caused the compressor to draw 17A continuously instead of 13A. It's a wonder the compressor survived. It was still running fine when I sold the coach last year, 3 years after I repaired it!

Stewart

[Volunteer]

I really appreciate the feedback here. I'm taking all comments to heart and will carefully try to figure this thing out.

Is my presumption correct that the "sticking relay" you're referring to is on the air conditioner's circuit board and not in one of my Discovery's fuse panels?

[GaryKD]

If the source of power is the coach circuit breaker panel and once the breaker is turned off the unit is still getting power, then the breaker panel must remain a suspect. For me, I'd change the coach circuit breaker first (easy and cheap fixes always get tried first).

[CaptBill]

Quote:

Originally Posted by Volunteer I really appreciate the feedback here. I'm taking all comments to heart and will carefully try to figure this thing out. Is my presumption correct that the "sticking relay" you're referring to is on the air conditioner's circuit board and not in one of my Discovery's fuse panels?

Yes, you are correct. If it is a sticking relay, (contacts welded together), that relay, also called a contactor, is on the A/C unit. It will be a relatively big relay, as it is switching 25A.

Do not work on a live circuit. Take steps to make sure that it cannot be made live while you are working on it. Make sure you know what you are doing if you take this task on.

[Volunteer]

I have to smile a bit because a good friend who also owned a "well experienced" Discovery once told me a man wasn't worth a flip unless he had at least half a dozen pliers and screwdrivers with burned places on them where they had found 120-volts.

I'm about three meds short of needing a pacemaker anyway so trust me, when I get up the nerve to look this problem in the eye again, the main plug will be pulled from shore power.

I'll replace the 30-amp main breaker first, then go up top to get the part number from the relay and see if I can get a new replacement. At least, thanks to all of you, it's a decent starting point since Summer is fast bringing those three digits to our Texas Hill Country temps.

[Luv2go]

Just in case you have to replace relays:

I replaced the relays on the PC board located in the air handler. I'm thinking this is the same PC board you removed the plug from that you mentioned in your first post. You remove the grate and filter to access it (I had a ducted unit, I assume you do too).

When I replaced the relay, I replaced all three relays on the board, ordered new ones from Digikey (no sense in replacing just one when they are all about the same age and condition). There were two T90S1D12-12, here: Digi-Key - PB110-ND (Tyco Electronics <!--Potter & Brumfield--> - T90S1D12-12). There was one T91S1D22-12 (which I believe was the compressor relay) when I searched tonight I couldn't find an exact replacement, i dimly remember having the same problem several years ago. Here's one that has the same pinout, I believe this is the one I used: Digi-Key - PB304-ND (Tyco Electronics <!--Potter & Brumfield--> - T9AS1D22-12).

The smaller ones just solder to the board, the larger one had leads attached to carry the high current.

I also found a stuck hard start relay, it was not on the PC board, you have to take the cover off the outside unit and open a cover on the side panel on the driver's side of the unit. I could not find an aftermarket replacement for this one, had to order from local RV dealer (I have a parts list for my unit which helped them find it), cost about $25. If you don't have a hard start kit, you don't have the relay, of course I didn't know I had one until I looked

You probably can find several manuals on the web, I have one which shows what the PC board does and the also one with the outside unit (at least the 7333 series I had), if you want them please PM me.

Stewart

[Volunteer]

First of all, Stewart, thanks for your time and the detailed information. The information I get from folks like you and the others who gave of their personal time to help me with this situation are very much appreciated.

We had a one-day heat wave last week here in the Texas Hill Country and I thought it would be a good time to do as one of you suggested ... test my main 30-amp front air conditioner breaker to see if it had wiped on me.

I pulled my front air conditioner filter holder, reached up and plugged the square power conector into the Coleman's circuit board. The "Guess What?" is, there was no hum from a running compressor.

The main Intellitec control was still in the "Off" position for both my air conditioners so I made sure the breaker was on, then went back and turned the front air conditioner on with the controller.

Sure enough, the front air conditioner came on and cooled my Discovery like it always has. When the thermostat was satisfied, the front air conditioner shut down, fan, compressor, and all. We've been cool since then and I haven't used it again but maybe all will be well until whatever stuck in the first place sticks again.

Interesting stuff, huh?

Thanks again for the feedback.