I have two things going on with my 97 Blazer.....

1st the 4WD switch isnt working. I replaced it a few months ago. No lights and no noise.....not sure where the fuses may be or how to check it.....

2nd If I place my AC on max AC it seems to come out defrost vents and when on regular AC and when I accelerate it changes the AC from the front vents to to the defrost vents.....I think its a vacuum leak but havent seen any that I can see.

Thanks in advance

 

The fuse for the switch is either behind the glove box or the fuse box in the engine compartment. If you pull it out and look at it to see if it's blown or not is the easiest way to check it. If it is blown you have a short somewere and will need to chase it down.

Next this is very common with older vehicles. Any number of vaccuum lines could be leaking, or any number of things could cause it. I've seen dirty air filters mess with vaccuum, and iv'e seen plugged cat's doing the same thing (rare though) The best thing to due is hooking it up to a vaccuum gauge and see how much vaccuum you have to begin with.