A/C fan toggling between HI/LO/OFF when thermostat set on AUTO

[CandWJackson]

My A/C fan toggles between HI, LO, and off when the thermostat is set to auto. It will run high speed on the fan for a bit, then switch to low speed, then turn off (like it should once the desired temp is reached) all within a minute. The A/C will stay off until the temp is above the setting, then the fan kicks on at either high or low, the compressor comes on and the fan speed switches between high and low again. It will do switch between high and low the entire time the A/C is running. DRIVES ME CRAZY!!! I have a Dometic digital thermostat and a Dometic AC. Is this normal operation? If so is it possible to set the fan speed to either high or low and have the AC turn on and off automatically? Advise is much appreciated.

 

[berky]

Just used my new North Trail (Dometic) A/C for the first time last weekend. It had some of the same weird behavior, though not exactly as you describe. I believe the fan behavior is purposefully designed that way by Dometic to optimize temperature control without excessively cycling the compressor.

I tried something I read in a manual I found for the thermostat : (1) press the mode button until the fan symbol displays, (2) press the up/down arrows to select either low or high fan speed, and (3) press the mode Hutton to switch to cooling. When I did that, the fan ran constantly and the compressor cycled as needed. YMMV.

 

[danemayer]

You can switch the fan to HIGH or LOW and it will run at that speed continuously. However, when the temperature drops and you switch to HEAT, the A/C fan will continue to run and to stop it, you'll need to change it back to AUTO.

 

[rjr6150]

Auto Fan
When “AUTO” fan is selected, the fan speed will vary depending on the difference between the temperature set-point and the room temperature. In “AUTO” fan, the compressor and fan will cycle ON and OFF with the thermostat.
When the difference is:
8 °F / °C or more
5 to 7 °F / °C
4 °F / °C or less
The fan operates on HIGH The fan operates on MED The fan operates on LOW

fron the Dometic manual