95 GMC Sierra Heater Problem

There is supposed to be some resistors somewhere close to the heater fan that run all the lower speeds. You will have to check the connections on those resistors.

The resistor pack you refer to is attached to the blower motor and held on by two screws. There's no checking the resistor connections though - the lans open up or the resistors themselves open up.

I have removed the resistor pack. I have ordered a replacement. Should be here in the next few days.

What identifies the resister pack as defective?

There are 4 coiled wires (resisters) in varying gauge (none burned open) and there was a diode that looked OK.

How do you test this thing if it looks like there isn't an obvious defect?

Changed out the resister pack and the heater works fine on all blower speed settings.

I still would like to know how I could test or identify what was wrong with the old unit.

No burn through on any of the resisters, the diode did not look fried. Connections looked okay and I had the old unit in and out a few times.

Thanks for your help.