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Old 04-03-2012, 07:57 PM   #1
Rivet Master
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1997 34' Limited
1970 27' Overlander
South of Atlanta , Georgia
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A/C help. It runs hot when it should be cold

OK, I am the first to admit I know very little about A/C systems. That said, remove and replace isn't tat hard. I have a 1997 vintage Dometic Penguin on the roof of my Airstream. The start capacitor appeared to have become weak, so I ordered a replacement start capacitor LNG with a booster capacitor. Sinc I was ordering stuff, I thought I might as well replace the relay as well. I don't think it is possibl to pu a capacitor in backwards, but could I have reversed the relay?

When I select A/C on th Comfort Control Center (CCC) the unit now blows really hot air! In fac it is ooler on the heat pump setting than the A/C. I used t heat pump in h morning to tak off th chill from overnight, bu hs afternoon when I wanted to cool the trailer I got a nasty hot blast instead of th cool air I expected. It also took what seemed to be a long time for the unit to com on.

All help is appreciated.

Craig and Carol
1997 34' Excella 1000
1970 27' Overlander, International
2009 Ford F150 5.4L
ProPride hitch with 1400# bars

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Old 04-04-2012, 12:32 PM   #2
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2005 39' Land Yacht 390 XL 396
Common Sense , Texas
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I recently had a simular problem in the bigger of the two A/C units on our recently traded for '10 31' Classic. Not exactly like yours, but simular.

The symtoms were the compressor unit would never shut off, and the only way you could stop it was to trip the breaker going to that A/C unit. However, the unit would cool well if the thermostat was set properly, but if the trailer ever reached the set temperature, rather than cycle the compressor, it would switch to heat mode and stay that way until the thermostat told it to cool again.

Since we were at a week-long rally and needed A/C, I only ran the unit in the heat of the day relying on the smaller rear unit at night, and then set the thermostat to such a low temp I knew it would never reach.

I called Dometic, and they told me they thought the problem was stuck relay, which I had already assumed. So, after returning home, I took the unit apart, comfirmed there was a bad relay on the board, removed it, ordered a new relay and a new start capacitor, installed them, and now the A/C unit is working properly. I would not recommend doing this board repair to anyone not experienced at soldering and board level work.

I believe this problem was caused by a bad start capacitor as I had noticed the compressor had a hard time starting in the past even though we did have good line voltage.

And no, the electrolitic start capacitors cannot be installed backwards. The relay that controls the compressor, at least on my unit, is a SPST (single pole, single throw), normally open relay, and so should work either way, however I did notice there was a land on the board that sends a power signal somewhere (I did not trace it out to find out where), so the wires should be installed as original. (I took pictures with my phone before removing the board so I could make sure I returned all the wires as they were originally).

Hope my expereince is somehow helpful to you.


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Old 04-04-2012, 01:02 PM   #3
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1991 34' Excella
Princeton , New Jersey
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Sounds like you hae 2 problems. If it is hotter in cooling than in heating I would assume that not only is the reversing valve to heat being held in the wrong position but you may also be calling for heat strip heat as well.

If both are in fact in heat mode that would account for the extra heating. If both are heating I would also look to the relay or relays that control the valve and the heat strip.

Sounds like they are using relays that are not rated for the current passing through them and fusing together. If the relays are fusing I would install a second high rated relay to switch the load and just use the original relays to control the new stronger relays.

I have seen this type of problem before on GM trucks where they install a relay rated for 1 amp and use that relay to control a fuel pump that draws 4 amps. A guaranteed service call just about when the warranty is over.
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles

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