95 GMC Sierra Heater Problem

Heater fan only works on the highest setting.
Replaced switch.
With tester, the fan is only getting power on the highest setting.
Any suggestions?

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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.

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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.
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-Mike-
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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?

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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.

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