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Tuesday, August 27, 2013

Air Conditioner Freeze Up


We have a 15 kBTU ducted Duo-Therm, roof mounted air conditioner on our coach. No heat pump. Here in Texas, with temperatures over 100-degrees every day, our A/C unit would keep freezing up leaving us without cooling for over an hour while it thawed. It puts out good cold air, but it will freeze up at least twice daily. Sometimes even in the middle of the night when the sun is down. This will happen whether we are parked in shade or sun. Any suggestions as to what we can do to prevent this? We have tried not using the ceiling fan, which is right in front of the return. We have tried having all the air dump into the area right where the unit is located via the shutter vent on the unit itself instead of going through the entire coach via the duct work; and other various things we have tried. Much to our dismay, nothing seems to work without, at some point, our A/C freezing up. Any ideas? Liz S., (Sunnyvale, TX)

Liz, all DuoTherm roof units have a freeze control device specifically mounted on the evaporator coils. The positioning of the control switch is crucial to proper operation. Have someone check for the proper positioning of the control switch and that it indeed measures no continuity when the ambient temperature is over 69-degrees. Pictured above is a diagram from the service manual to help you understand the location of this switch. It’s entirely possible the switch has come loose from its mounting or is faulty. This freeze control is a thermally-activated switch of sorts that closes once the temperature of the evaporator falls below 49-degrees F. Once closed, it will re-open when the temperature rises to between 61 and 69-degrees F. If it fails to open and the temperature is above 69-degrees, it needs to be replaced. A simple continuity test and temperature measurement should quickly reveal the status of your freeze control device.

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