hello I don't know if this is were this would go but I think it is. Anyway I live in michigan and it has been raining and geting cold here and I whent to use my front window defroster today and it didn't come on there is no air blowing out of the vents. it is the same when I try to use any seting heat, ac, vent. So my ? is what is going on. Also the other week when I was driving at night the little lite in the rear defroster switch whent out don't know if that is important or not.

 

The front controls are vacuum powered I believe. Look under the hood for a vacuum line that is unhooked or broken. Hard to see sometimes look close. Rear defog has a timer in the switch, goes out after a couple minutes. Think this runs on a circuit breaker in the fuse box under the dash, no fuse on it. (edit, your 91 Firebird may have electric heat duct controls, not sure. Sorry if I'm wrong)

 

It may be the ground wire for your blower motor. That was my problem

 

k thx I will take a look at those things