Chevrolet Repair: 1996 ac/heater switch problem, resistor pack, chevy 4x4

Question
I have a 1996 chevy 4x4 k/1500 5.7 when I run my heater and a/c it will only run on high not low or med.Yes I have replaced the fan moter cause of a sqweek when it is turned on.when i turn it to low or med will not blow anything but turn it to high and it runs good .Can you tell me how to fix this and is there a specail switch for this you have to replace.

Answer
Hello Rick,
That is the classic symptoms of a bad resistor pack.
Adding resistors to the circuit is how the speed is reduced. No resistors are used in Hi.

To get to the resistor pack, remove the glove compartment...door, pouch, and all, and behind there, on top of the heater housing, you will see some wire connectors that seem to be mounted on top of the housing.

The one with about five wires, actually protrudes down into the housing, and is the resistor pack. It is inside the housing so that the air flow can cool the resistors.
Just remove it, and you will probably see the open wire, but even if you don't see an open wire, it could be that diode on the pack.
Replace the pack, and that will almost surely fix your problem.

Van