A/C Short Cycling

[JanAndBill]

We recently bought a used 2019 trailer, with Dometic air and a single zone Dometic thermostat. On "auto", during the day, it seems to do okay, but of a night the fan and compressor comes on runs a couple minutes, then shuts off. Couple mins later it will kick on again, only to repeat the process. Drives you crazy during the night. The only way to avoid the constant on/off is to turn the fan to Low and let it run continuous. The compressor will cycle on and off as needed. I've never had one of these thermostats, but have read they can be problematic.

Any ideas????? Is this normal????? Troubleshooting ideas???

 

[lynndiwagoner]

Try resetting the thermostat...that works for me. There is a procedure in the book.

 

[danemayer]

When the thermostat senses that ambient temperature is approaching the set point, on AUTO, it'll slow the fan down. When set point is reached, it shuts off. On ours, on warm evenings, it'll cycle the fan and compressor back and forth to try and hold the desired temp. So it sounds to me like what you're experiencing is pretty normal. And yes, turning the fan to either HIGH or LOW will make the noise more constant as you're less likely to notice the compressor changes occurring in the other room.

Just remember to set the FAN back to AUTO before trying to use the furnace. If on HIGH or LOW, the A/C blower will run right along with the furnace.

 

[JanAndBill]

Try resetting the thermostat...that works for me. There is a procedure in the book.

Already tried it. Didn't make any difference.

 

[JanAndBill]

When the thermostat senses that ambient temperature is approaching the set point, on AUTO, it'll slow the fan down. When set point is reached, it shuts off. On ours, on warm evenings, it'll cycle the fan and compressor back and forth to try and hold the desired temp. So it sounds to me like what you're experiencing is pretty normal. And yes, turning the fan to either HIGH or LOW will make the noise more constant as you're less likely to notice the compressor changes occurring in the other room.

Just remember to set the FAN back to AUTO before trying to use the furnace. If on HIGH or LOW, the A/C blower will run right along with the furnace.

On auto during the day, it will cycle off (fan and compressor) when it reaches the correct temperature. Depending on ambient temperature it miIght stay off 5,10,15 mins or so before it will kick on. Of a night it drives you crazy with the ON/OFF routine every 2 or 3 mins.

Is there a way to adjust the temperature differential???? It seems like it's trying to hold the temperature to exact.

 

[danemayer]

On auto during the day, it will cycle off (fan and compressor) when it reaches the correct temperature. Depending on ambient temperature it miIght stay off 5,10,15 mins or so before it will kick on. Of a night it drives you crazy with the ON/OFF routine every 2 or 3 mins.

Is there a way to adjust the temperature differential???? It seems like it's trying to hold the temperature to exact.

You can change it between a 1 and 2 degree differential.

• To set the temperature differential the system must be Off.
• Press the“―” button and, while holding it, also press and hold the On/Off Mode button for three seconds.
• Release the On/Off Mode button.
• Then release the “―”button.
• Press the“+” button to toggle between “d1”and“d2”, “d1” for 1 degree F differential and “d2” for 2 degrees F differential.

 

[wdk450]

Any chance this is a freeze sensor problem???

 

[JanAndBill]

You can change it between a 1 and 2 degree differential.

• To set the temperature differential the system must be Off.
• Press the“―” button and, while holding it, also press and hold the On/Off Mode button for three seconds.
• Release the On/Off Mode button.
• Then release the “―”button.
• Press the“+” button to toggle between “d1”and“d2”, “d1” for 1 degree F differential and “d2” for 2 degrees F differential.

I need to check, but I believe when I reset it, that it defaults back to d1. I need to recheck that.

 

[JanAndBill]

Any chance this is a freeze sensor problem???

I would think its possible if just the compressor was cycling, but it's not. The fan and compressor both cycle on and off.

 

[travelin2]

Ours does the same when the indoor and outdoor temperatures are near the same as the thermostat set temp. The only way I have alleviated it is to change the set temp either up or down and deal with it or just shut one off. We rarely have both AC on overnight. That way the single one has to work harder ie run longer

 

[JanAndBill]

Ours does the same when the indoor and outdoor temperatures are near the same as the thermostat set temp. The only way I have alleviated it is to change the set temp either up or down and deal with it or just shut one off. We rarely have both AC on overnight. That way the single one has to work harder ie run longer

Changing the temperature setting works for a little bit, but then does the same thing. Haven't had a chance to check the temperature differential, but I'm leaning toward that as an issue.

 

[marknewbill]

My new Dometic thermostat in my 2021 Heartland Pioneer single zone also has an issue, may be the same thing. when it is on manual high or manual low, it works as desired. But the Auto fan is pretty much useless. once the temperature becomes normalized to the set point, the fan begins hunting between low and high every few seconds. I fear this will damage something to keep cycling the fan on - off - on - off where the off is what happens in between high and low. but the compressor stays on the entire time until the temp decreases below the set point. I called Dometic, and they said that operation is normal. I don't buy that. it should require several degrees of change to switch speeds, and then require another few degrees of change to switch back. in that way it wouldn't hunt continuously.

IOW, there is no real auto setting. I just have to disregard its existence, or try another thermostat. any recommendations to replace it or fix?


Adding the D1 and D2 only apply to the heater as best i can tell. It would be nice if that worked for the AC as well.