I have a 1986 f150 4x4 it has add on AC The blower motor will work on low and high speeds for heat not medium. the AC blower motor (different motor) works on all 3 speeds. So it can't be the switch I assummed. I checked the continuity on all 3 terminals from the resistor and recieved a reading in all 3. Can I check the plug that goes into the resistor to make sure that is ok? Can it be the blower motor for the heater? Motor is 6 months old. Thank You for the help Bill

 

That resistor pack on the factory blower is a common point of failure. They are pretty cheap. Even though you got a reading across them, one may be out of tolerance. Does your aftermarket AC use the same switch as the factory?

Bill

 

Bill, yes the aftermarket AC does use the same switch. That is why I thought it could not be the switch. I will go purchase a resistor and see if that is the problem. Thanks for the help. Bill

 

> Can it be the blower motor for the heater?

The motor is usually very easy to test. Remove it, put it in a vise, and attach power leads to it. My test leads are fused (15 amps) and about 15 feet long, so I hook right up to the truck battery. The motor should be tested in its horizontal position.