Cab air conditioner fan control

[C21Tiger]

I have had to replace the cab air conditioner fan control twice and now it has failed again. The failure mode is only high speed with no lower speeds. Any suggestions other than replace the switch again or is there a way to be able to check voltages and trouble shoot backwards toward a connections or ??

[DaveFL]

Trace wires from back of unit, mine had a fuse on the passenger side left of the radiator. Don't know if they changed it when they switched to the workhorse chassis.

[woodytwo]

Same on mine 2005 30 slide

[J. Morgan]

Is it the switch or the resistor in the duct?


Brevi tempore!