More Basement Air Woes

[JimNCheryl Domenoe]

I am becoming disillusioned with the air conditioning system on my 2000 Marquis.  When I bought the coach the a/c was not working.  At the recommendation of BCS and others on the forum, I took it to the shop in Bend to have it looked at.  It turned out that one compressor was bad, the control board was fried and the copper lines were broken.

They replaced the #2 compressor, added flexible lines, new compressor vibration isolators and replaced the control board with new relays.  The fix took three days and cost almost $2800.
 
Since it was in October, I have not really had a need to use the A/C much, even in Southern California. I have now begun to use the A/C and have found that it really struggles to keep the coach cool, and it seems it never keeps it as cool as we would like.  The system seems to run constantly and it rarely, if ever, reaches the set temperature, which is generally around 78-80 degrees.  The outdoor temperature has been in the upper 80s and there is a considerable amount of humidity where I am.  The other day I noticed that when the system was up and running, I would hear the compressors kick on and cool air blows out, but I would hear the system bog down slightly on a regular basis.  I didn’t pay that much attention to it at first, thinking it was just the second compressor engaging.

During the night when all was quiet and listened closer, I could hear it bog down for 1-3 seconds.  This occurred like clockwork every 60 seconds or so.  The air coming from the ducts was not all that cold either.  I then got the idea to check the CMP to see what was going on.  When I checked the AC Amp reading it would read anywhere from 7-11 amps on leg one. That is, until that bog kicked in.  At that point, it would kick up to 27 and then 50 and then the letters HIGH (in red) before it kicked back down to the 7-11 amp range. I also checked AC Amp on leg 2 and it was anywhere from 4-12 amps.
 
I called the A/C place in Bend and they could not really diagnose it over the phone with any certainty.  They suggested something was bound up.  He suggested not running the AC until it could be checked.  That would be a bit of a problem since I live in Southern California, but I am in eastern North Carolina right now.

The tech suggested turning the system fan on the thermostat to low to keep the second compressor from coming on, but I tried that and there was no difference.  Even the amperage on leg 2 never changed and it appeared that at 11 amps, the second compressor was working, even on the low fan setting.

Another thing I find interesting is that the Voltage Leg 1 gauge on the CMP reads 0 all the time.  Leg 2 is always around 116-120. Does this seem right?  If not, could it have anything to do with the air conditioning system operation.

My question is, does anyone have any ideas as to what it might be.  Secondly, does any know a place in the area that might be capable of working on basement air conditioners?
 
I can’t imagine heading back to California with no air conditioning, especially since I still have four weeks left on my trip.

[Steve Huber Co-Admin]

Jim,
I'm far from an AC expert but we've got the same AC setup as your coach. Leg 1 voltage of 0 on the CMP is not right. Since you have leg one current, obviously there is voltage. Check to see if the CMP still reads 0v when the AC is turned off. The extra high leg 1 current when the 2nd compressor turns on is wrong too. It should not vary much if at all as the compressor on leg 1 should be unaffected by the 2nd unit startup. Does the leg 2 current drop to 0 when the second compressor is off? It should read 0 as the second leg only supplies the 2nd compressor (I think). If I had to guess, I'd suspect the control board (accessible behind the panel on the left front side of the water bay) or a wiring problem when they worked on the unit. If you access the control board, check to see if there are overheat indications near / at where the connector is soldered to the PC board.
Good Luck, Steve

[Gerald Farris]

Jim,
First if your CMP reads 0 voltage at all times on leg 1, but it reads amperage on leg 1, that is a malfunction in the CMP and should have nothing to do with the A/C unit. However, you should check the system voltages with a good meter before proceeding with the modification below.

From you description of the amperage usage of your A/C, it sounds like the #1 compressor is locked. If so, the only temporary repair that you can make is to disconnect that compressor at the unit and depend on the #2 compressor for cooling. You have to disconnect the bad compressor at the unit instead of turning off the breaker for it because the fan runs on the same circuit. Also leaving the #1 compressor in the circuit can be a safety issue because the high amperage draw will overheat the circuit components, and possibly cause a fire issue although that is a remote possibility.

After you disconnect the #1 compressor, the #2 compressor alone will lower the interior coach about 10 degrees below the exterior temperature, but since the #2 compressor only runs if the thermostat is set at least 2 degrees below the interior ambient temperature, you will need to set the thermostat at least 2 degrees below the desired temperature.

If that does not make sense to you, call me and I will walk you through the process.  I am currently in the Central Time Zone.

Gerald   

[Edward Buker]

Jim,

Because you have current being read and it varies on the CMP panel for both legs I would not worry about the voltage reading being zero, that must be in error. If you have two breakers that feed the AC system on your main breaker panel you could measure the voltage there with a meter to check the feed voltage. I do not know if they use a sub panel for the breakers that feed this AC unit or if it is in the main panel but wherever it is fed is where you would try running with one breaker on and one off. Given everything else in the coach is working you must have proper voltage in each leg.

It would seem that you have a locked compressor rotor with an auto resettable thermal breaker to protect the compressor that is kicking on and off. I say that because of the 60 second repeatability of what is happening. It is also possible the control circuit on the circuit board monitors and has control of this protection timing but that seems less likely to me. It is not a good situation to allow to continue.

I do not know if the system would run with one breaker off (the one that runs the locked compressor) but if it would that would be an option. If not the folks that worked on it may be able to tell you what wire to the compressor could be disconnected and taped off as a temporary measure. There may be other folks on the forum that have worked on this unit that have some wiring insight. My coach has roof airs so I am not familiar with the AC wiring for your unit.

Basically you want to find a way to disconnect what is likely a black wire that feeds the compressor with the locked rotor and hope that the control circuitry is not sophisticated enough to sense the non working compressor as an issue. It seems unlikely that it would be that sophisticated. You will have limited cooling. On the east coast Alliance Coach in FL would be one place that would be an option.

Just read Gerald's post and he has the answer that you need, basically we are saying disconnect the AC feed wire to the bad compressor and he has the specific info on how to do that with this type unit....

Later Ed

[David T. Richelderfer]

Your a/c problem sounds almost identical to the problem our coach had last year.  There is a difference in that our coach has three roof units as compared to yours I believe having a basement unit.  But an a/c is an a/c, and they all run pretty much the same.  It sounds like one compressor has frozen and will not turn on.

http://beaveramb.org/forum/index.php/topic,4429.msg33347.html#msg33347

[JimNCheryl Domenoe]

Thanks for all of your timely replies and suggestions.  I believe the suggestion to remove the #1 compressor from the electrical system is what I will try. Gerald, I will call you for direction.

Florida is going to put me way off course so I will try this solution and see if it will get me through this trip. I'll keep you posted.

[JimNCheryl Domenoe]

OK, I got the #1 compressor disconnected from the electrical system as Gerald suggested and the air conditioner at least functions, albeit at a 50% reduction in cooling.  Hopefully the weather will cooperate for the remainder of the trip so we don't roast.  If it wasn't for our dog, I wouldn't be too concerned.  We often take side trips while leaving him in the coach and with inadequate cooling that just won't be possible.

I may try to get to a shop on the way home to get it repaired if I can work it out.

Thanks again for your assistance.

[JimNCheryl Domenoe]

Update.  I ran the A/C today to keep things cool before it got to the heat of the day.  We left it running for a couple of hours while we went for a walk.  When we got back it was nearly 90 degrees inside, while the outside temp was only in the around 75, and the coach is parked in the shade of the trees.

Not sure what is going on but I will need to find a shop to get it repaired.