I have a 2002 Blazer...the two door model. Just today the high speed fan stopped working, it was acting a little strange yesterday...when I selected it, it didn'tcome on at first and then suddenly did...worked fine the rest of the day....there were a couple of times it sort of faltered buyt then came back on. All the other speeds work fine. Am I looking at a bad switch or is it the resistor board that I need to replace? I have had to replace it once before....a year ago I had to replace the blower motor.

 

On high speed, the resistor is bypassed and the voltage to the blower motor goes straight through the relay on the firewall. I would start by checking/replacing that. There's also a 30A HVAC fuse under the hood that should be hot at all times. I would check that, too. Don't confuse it with the other HVAC fuses that are 10A and 20A and should only be hot with the ignition on.

 

Im having that exact problem... ive checked the fuses and no bad fuses... where is that relay located?