Heater Fan not working when Engine Heats Up

Hey Guys,

I have got a really weird problem with my 99 Tahoe. It seems with the colder weather upon us, the truck has really been acting up a lot.

Most recently, the heater seems to be intermittently working. I can get in it in the morning, and start it up, fire up the heater and the defroster and everything works great. I'll drive for 10-15 minutes and the engine will get warmed up and the heater is blowing hot air and everything is great. Then I'll stop for coffee and shut the truck off, and when I come back to the truck I have no fan whatsoever. None of the settings work - 1-4. I have tried wiggling it and it does nothing.

I'll leave the fan on (despite the fact that it doesn't work) and I'll be going down the road and it will randomly kick on again. It seems to be that when the engine is warm the fan doesn't want to work at all.

Any suggestions as to what the problem might be? I'd attempt to fix it, but I don't even know what to fix?

Thanks in advance for your suggestions.

-Joe
'99 Tahoe
5.7 Liter V8
95,000 miles

sounds more like the switches, my 99 did that, i went to ebay and found one and it worked great after that, mine did exactly like what you described and they did not line up, i could be at high and it would only be at speed 3 enless i moved it around.

Check the connectors and wiring at the blower itself and the relay. The fan draws a lot of current. If the connectors are loose or the relay contacts are bad, the added resistance and high current will begin to heat up the point of resistance, enough to where not enough current will flow to operate the fan motor. Could be a loose connection, bad wiring, motor, relay, or switch.

This morning I started the Tahoe, and turned the defroster on, and nothing. No fan action whatsoever.

I tapped on the heater down by the passenger's feet with my hand a little bit, and voila! the defroster started working. I'm guessing there is some sort of a short or bad connection down by the heater core / fan motor.

Typical GM electronics I guess...had the same problem with my '97 Grand Prix 2 winters ago.

gotta love that gm quality control!