Thermostat Fan Setting

Basically........NOTHING

Low fan....almost as noisy as high fan
Low airflow can cause 'icing' of evap coil in humid weather

IF fan is in either Hi or Low setting and you run furnace the FAN (A/C Unit) will also run
FAN setting is for A/C Unit....thermostat controls both A/C and Furnace

Set the FAN in AUTO and forget about it :B

I use low at night to drown out noise.

If you have a WALL tstat, there is no icing or freeze up that can happen. Wall tstat controls have a freeze sensor in the evap coil. On LOW, you will get slightly colder output air. This is because the air flow is slower thru the Evaporator and has more time to pick up the cold air. LOW is better at night to keep the fan noise lower to sleep. Doug

When you run it on auto, does it run on High or Low setting, or maybe both?

It depends on the system setup and maybe how things are wired. On my RV the thermostat had separate switches for High and low speed and for auto and constant-on, so you chose what speed it would run on auto mode. I would guess typically it's high, but a bit of experimentation should make it obvious.

The fan speed only applies to the air conditioner; practically all RV furnaces have a single fan speed.

Cocky_Camper wrote:
When you run it on auto, does it run on High or Low setting, or maybe both?

Some models on Auto, the Hi Fan runs first and then as the preset temp is close, will go to Lo fan and then OFF once the preset is reached. Doug