Dometic roof air

Question

Compressor relay was stuck on so replaced control board.The unit worked good  until down to set temp and then compressor would cycle on and off every 20 seconds.Replaced thermostat and the cycling improved to every 60 seconds.Unit worked OK for a week and the relay stuck again.My thinking is that there should be a bigger temp gap between the compressor off to back on again.My fear is that it will keep up the cycling and ruin another relay. Any other thing besides thermostat to cause the cycling? Freeze sensor? Thinking hard about a round Honeywell...

chris_bryant · Answer

Which thermostat? If it is the old style analog, you can bypass it by jumpering between the cool terminal and ground.

wrgrs50s · Answer

Are you sure it's the compressor cycling or the low and high fan cycling, because there is a well known issue with the dometic thermostats where the fan speed will alternate low to high in quick increments when set in the auto mode. If the thermostat fan setting is set to low or high instead of auto, it eliminates that issue. Mine has had that issue and I cannot find a fix so I just run the fan setting on high all the time.

30sweeds · Answer

wrgrs50s wrote:Are you sure it's the compressor cycling or the low and high fan cycling, because there is a well known issue with the dometic thermostats where the fan speed will alternate low to high in quick increments when set in the auto mode. If the thermostat fan setting is set to low or high instead of auto, it eliminates that issue. Mine has had that issue and I cannot find a fix so I just run the fan setting on high all the time.Definitely the compressor.Fan is on high constant.Fire up the AC when MH is super hot,compressor runs,fan on high.Works really good till down to set therm temp...then the compressor cycling begins.Might have thought it was normal operation but have burned up 2 compressor relays in 2 wks of operation.

30sweeds · Answer

Update...ended up being a faulty freeze sensor.Bought a new digital thermostat and board that came with a freeze sensor.Stuck the freeze sensor in and since the plug was the same as the old analog unit,plugged it in and gave it a try.Got down to temp and cycled when therm called for it,not constantly on and off.Apparently the freeze sensor is wired in series with the trigger wire to the relay.Finished the digital install and love it!

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