Trouble-Shooting Your Air Conditioner

Here are some problems you may encounter with your roof-top air conditioner:

Won't re-start

This is called compressor lockup. It happens if you turn the a/c off and then try to turn it back on again within two minutes or less. It can damage (burn out) the motor if you force it to try to turn a compressor that doesn't want to turn. That's why surge-protectors/power conditioner units such as the Progressive Industries EMS-HW30C that many RV'ers use include a two-minute-plus startup delay - to protect the air conditioner's compressor in case of a power loss and immediate restart.

If you're running your generator to power the a/c and shut the generator down and then restart it with the a/c still turned on, the same thing may happen. It may also trip the circuit breaker on the generator, so check that.

If you turn the compressor off by dialing the thermostat switch to a lower setting and then turn it back to a higher setting, the a/c may shut down. Wait several minutes before selecting a higher temperature.

Icing Up

If your Dometic air conditioner is icing up, check to see if your model has an ice sensor over the coils to prevent that from happening. Some sensors need replacing and some need to be checked for proper placement. If you are having this icing up problem, call Dometic and see they will send you a new sensor. Dometic may recommend placing the sensor in a different location across the coils. Also, check your Dometic manual for information on the sensor.

Leaks into Coach

If your air conditioner is leaking into the coach, proceed to troubleshoot by removing all of the A/C's interior plastic trim so you can see the roof penetration and the edge of the roof gasket. You should be able to see if the leak is coming through the roof (the wood will be wet along the top edges of the inside of the roof penetration) or out of the interior of the A/C. A roof leak would indicate a loose or bad gasket. Water coming off the A/C body would suggest a plugged condensate drain or a cracked condensate pan.

Another quick test for a bad roof gasket is to pour a couple of gallons of water on the roof. Do this with the interior A/C trim removed so you can see an active leak up close and personal. If it leaks immediately, get up there and dry the roof with towels. If not, leave it for a longer test. There should be no leakage, no matter how much water is poured on the roof.

Some rooftop A/C's condensate drains cannot be easily accessed by just removing the shroud. These units require disassembling the top of the evaporator housing to get at the clogged drain(s).

One other cause of A/C leaks is the hold-down bolts. Check to make sure the bolts are tight.

Blows out small particles

My Dometic Brisk Air Duo-Therm air conditioner has recently started blowing out small dark gray particles. It happens both when cooling and when using the heat strip. Replacing the filter didn't help, and the old filter was in good shape (not disintegrating). The particles vary in size up to about 1 square millimeter. They're dry and leave no residue.

Solution: More than likely they are dust particles that have gotten past the inlet filter and built up on the fan blades. When built up enough (takes several years) they will break loose from the blades (and other surfaces in the airway) and blow out. Try removing the cover of the roof AC section to uncover the fan housing and wipe each blade. Also vacuum all areas in the airway. Maybe a new filter element a little larger might help after the cleaning.

Contributors: Ramon, Larry Wade, Chris Horst, Andy Baird, Edward A., Mike Coachman

Revised: 2 Nov 11

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