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Roof Air Conditioner Intermittant

Yahoo Message Number: 88386
My front roof air conditioner blows and cools fine for about 10-15 minutes, then the fan continues to blow but, I can hear the compressor stop and then of course the cooling quits. This happens especially if the ambient exterior temp is over the high 90 degree range (when we need it the most!). I have to shut it down or it begins to blow warm air.
If I wait about 10-15 minutes, I can start it up again. Then, the above scenario repeats.
I replaced the blower fan motor last year.
We have clean 50 Amp power.

Any Ideas for diagnosis would be appreciated? Daron Hairabedian, 98 Allure 30226

Re: Roof Air Conditioner Intermittant

Reply #1 –
Yahoo Message Number: 88391
If the unit comes on and you can hear the compressor running, and then it cools at high fan, it could be the "freeze switch" aka freeze sensor.
You can test this by putting a jumper wire between the two terminals for the "freeze switch". (On my unit, this can be done from inside the rig.)

D Vogel

06 Allure 31409

Re: Roof Air Conditioner Intermittant

Reply #2 –
Yahoo Message Number: 88395
Daron - It's possible your compressor motor is shutting down on thermal overload. Compressor motors are often capacitor start capacitor run. A faulty off value run capacitor may cause excessive heating. I burned up parts in my A/C unit. Chronicle is here: http://www.muniac.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=103#Post103 Maybe this will give you an idea of where to look. Low AC line voltage can also cause excessive heating. Make sure it's proper at the A/C unit.
Not sure what A/C unit you have but all of them include thermal protection devices of some sort. You need to obtain a service manual and study the schematics. Locate the thermal protection device(s) and find out which one is tripping. That will give you a good indication of where the problem(s) are. The compressor motor may have one inside the windings. Of course, at 15 years old the unit just might be shot. Good luck.

Best - Scott

2006 Allure 430 40' #31349

(Bus-Stead Lemon) My Allure Page http://www.muniac.com/Allure%20Page.html

Re: Roof Air Conditioner Intermittant

Reply #3 –
Yahoo Message Number: 88398
Daron, I have similar symptoms on the front AC (Dometic) of my 03 Intrigue. I was advised my a tech to put a thermistor on the unit rather than rely of the one on the climate control unit (lay it in the air intake area), but I haven't located one yet. Let us know what you find out please.

2003 Intrigue #11509
 

Re: Roof Air Conditioner Intermittent

Reply #4 –
Yahoo Message Number: 88407
Daron,

Had exact same set of conditions. Puzzled more than one A/C expert because they could not duplicate the symptoms. Finally found a real experienced A/C guy who quickly showed that the freeze detector was giving false indication of freeze-up at condenser coil. Hence compressor shuts down and fan goes to max trying to remove ice from coils. After some period (tens of minutes) the faulty freeze detector resets and A/C comes back on. Replace freeze detector and A/C system runs great again and has kept running normally for months. Runs to mind it was about a $30 part and 10 minute job to replace.

Jim M.
SOB