Yeah, it seems you might be getting AC fan operation confused with furnace fan operation. The only reason for the furnace fan to operate without heat being generated is for about a minute before the burner ignites to clear any accumulated propane from the combustion chamber and for about a minute after the burner shuts down to cool the components. When I cycled the temp up to 90 and back down to 50 all I did was fool the furnace into thinking it was going to light the burner, start the 1 minute "fume clearing" timer and then lower the temp requirement before expiration of said timer.
The A/C fan can be operated without actually running the cooling compressor for the purpose of moving air around in the RV. However, AC fan operation requires shore power. The relay that controls AC fan operation does operate on 12VDC and you are probably hearing that click.
I have never seen a furnace fan that will run without producing heat except for the short time before and after burner ignition. In fact, on my last motorhome I intentionally modified the furnace (with the addition of a switch) to provide fan operation without generating heat so I could move house heat produced by electric space heaters from the house to the storage compartments below the floor. That way the junk in the storage areas did not freeze in the winter.
