Ok I have a 95 blazer and as of three days ago the ac has been acting funny. When I turn down my radio and put it on mute, my acsounds like speaker hiss and the ac is'nt even on nor the radio. And when I put the ac on max, it just blows in the lower vents but it used to blow in the upper ones too. Any suggestions?

 

Sounds like you have a vacuum leak. Almost all of the actuators for the HVAC system are controlled by vacuum supplied by the engine. The hissing you hear is mostlikely that leak. See if you can't track it down just by listening. That would be the easiest approach.

 

Ok, so its nothing serious, well thats good news. I will try later today because it is t storming now but thanks a lot for the help, I will post later on my findings.

 

I took a small look not to long ago and I tried listening in the engine compartment but the engine has to be running to hear the leak so it makes it diffacult. I went inside and listened and it sound like the hissing is comming out of the top two vents so I wonder could the leak be somewhere in the dash or something?

 

If you can find an old stethoscope they are really helpful for pinpointing these kinds of noises... alternatively a paper funnel or really any sort of hollow tube like a piece of PVC pipe in a pinch. A real mechanic's stethoscope is anywhere from $10-$30; I picked up an old doctors one at a yard sale for a quarter.

The acutators are generally somewhere inside the daashboard so you should be listening inside the car.

BTW a vaccum leak should be fixed as it can lead to poor gas mileage and driveability issues.

Good luck

Jeremiah