Just the other day, I went to turn on my A/C and it wouldn't blow from the vents. I'm pretty sure the compressor is coming on because of the drop in engine speed but I haven't actually looked to make sure but I'm almost postive. So if the compessor is coming on, then they mode selector switch is probably good right? A couple days after it stopped working, the blower motor came on for a couple of seconds and hasn't come back on since. I'm pretty sure that it is probably the fan speed selector switch. Any thoughts?

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91 Forest Green Firebird with TBI 305 3" Edelbrock Cat back, Dynomax headers, matched flow fuel injectors, injetor spacer, throttle body spacer, MSD Blaster coil, 8.5 mm MSD wires, 160 degree stat, Hypertech Thermomaster chip and low temp fan swich

 

Could be the blower motor itself. I had a fan motor which would work sometimes. Turned out I had to replace the blower motor. Could be a corroded switch too, of course.

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88 GTA 5.7 TPI Charcoal Grey Bone Stock except for loose muffler which makes it a bit louder than normal.

 

I just had this same problem and it turned out to be something loose in the power connection. There are 5 or 6 bolts (7 mm) you need to take out around the front of the blower assembly (have fun with the bottom one!) and then you can pull the fan and the motor out.
I went ahead and pulled it out and blew out the dirt that had accumulated. Then with the key in the ignition turned on and the ac on I could move the power connection a little and the speed of the fan would go up or down or stop all together. I cleaned out the connections but that did not change anything.

The thing that finally fixed it was to put it all together and wedge a small piece of wood under the power connection to keep some tension on it. And since I cleaned out the motor and sprayed some wd40 on it, it blows alot harder now. Also replaced the 7mm bolts with 5/16.