My heater control consists of a fan speed dial with 4 speeds to choose from. Then there are two slides, one to choose floor, vent, or defrost, and the other to choose temperature (- to +). The heater has always worked on only the highest speed setting in the past. The last few times I used the truck the switch seemed to have trouble engaging the blower when turned to the highest setting-It seems that I had to put pressure on the switch (as if i were attempting to turn it past the highest setting) in order for the blower to kick in. Now I have no heat at all. Does this sound like a problem with the switch? Perhaps I could bypass the switch. From reading some other threads, having only the highest fan speed seems to be a resistor pack or relay problem. It is not important to me to fix the lower speeds-if i could just have the highest setting work again i would be more than happy.....this is simply a yard truck used for plowing.

 

Sounds like the switch. New Control Module.