My ac blower fan only works on one speed, low, which is bad news in Texas in the summer. Is there a way to fix this or does the blower control need to be replaced or what does need to be replaced to make it work on all speeds?

 

https://www.dieseltruckresource.com/...m-t301306.html

 

Ok, I'm not sure exactly how these things work. Does the motor have 3 speeds and the switch accesses the circuit to each motor speed? In that case I would need a new blower motor. Or does the switch control 3 different currents to the motor, each raising motor speed more? I'd like to know how this works so I understand what is going on in there.

 

The motor has one speed. The switch in the dash sends power out through a series of wire resistors(one for each speed, mounted in the duct work to keep them cool) that increase the resistance in the circuit to reduce the voltage and slow down the motor speed. These resistors can burn out over time, or sometimes the switch itself will go bad. An ohmmeter will quickly tell the story.

 

Typically, if the motor spins, it is fine. I know the fan speed switch on my unit is going out. If I lower the speed, I have to jiggle the switch to make contact to get the fan to run at high speed.

 

Is it possible to replace those resistors? If so, would the values be printed on each resistor? Any idea where I can find these resistors in the ductwork?

 

It probably is the resistor it's right in the box by the blower

 

By the motor in the engine compartment or in the interior of the truck?

 

Look behind the glove box for a 6 or 7 blade connector on something bolted to the heater. That something is the resistor block.

Before you get too carried away, look at the back of the heater speed switch. I'll bet you'll find a significant amount of charcoal. There's your problem. When the switch gets old, it heats up, fails, and takes the connectors with it.

 

Mine had the same issue. It was the fan speed switch. Replaced it for about $8. Mine had some burned marks on the back.

 

Thx for that tip J. Thanks for all the help everyone, I'm going to dig into this sucker.