Sounds like you have the square dometic digital thermostat. When you press the button to activate the fan, you have three choices.
Au: Automatic. In this mode the fan only comes on when the A/C compressor comes on to cool the coach.
Hi/Lo: when either one of these is chosen, the fan will run continuously when the A/C is chosen and the compressor will cycle on/off depending on temp setting. In this setting the A/C fan will run on the selected speed when the furnace is selected.
To change the fan options, press the bottom button until the fan LED lights. Then using the temp up or down cycle thru to the desired setting. If you DONT want the A/C fan to run when you use the furnace choose Au (automatic). This only applies when you have 110VAC supplied to the trailer. If your not plugged in to any 110 power source, the fan wont run as it is an AC current fan.
All of this should have been explained in your walkthrough/orientation. It never ceases to amaze me how many employees doing them don't know and don't ask.
2012 Copper Canyon 273FWRET being towed by a 1994 Ford F350 CC,LB,Dually diesel.
Airlift 5000 bags, Prodigy brake control, 5 gauges on the pillar.Used to tow a '97 Jayco 323RKS.
Now an RVIA registered tech. Retired from Law enforcement in 2008 after 25+ yrs.