Blower problems

Just the other night, my blower stopped functioning properly. In all modes, vent, heat, defrost etc., the blower was blowing air out of the defrosting vents. In addition, there was a hissing noise coming from behind the selector panel for the thermostat control. I took the dash off today and pulled at the thermostat control panel and couldn't find any problems. I did some twisting and turning w/ the panel and somehow the blower was working normally again but as soon as everything was back together it was back to hissing and blowing out the defroster vents. I have no clue what is wrong please help!

Not sure about the Blazers, but I think the heater/ac control panel are very similar to my p/up and I had a problem very similar to this which I found out is a very common problem on certain years models. Although I'm not sure what year model you have, or if the control panel is similar to mine. However, for what it's worth, my problem was the fan switch itself. (My fan swith has like 6 positions: off, 1, 2, 3, 4, 4, and 5) If your fan switch sounds similar to what I described, might be worth checking it out.

FYI: dealerships will try seling yopu the whole ac control assembly and say thats the only way to replace that one switch that is bad. Of course that assembly was like $170 but I delivered parts and found an honest parts guy who sold me the one switch I needed for approx $12 to $15. If your Blazer is a '96-'98, I think the controls are identical to my p/up

you have a vacuum leak which is causing the hissing sound.

Check all vacuum hoses going to the controls, everything other than the fan is vacuum controlled.

you have a vacuum leak which is causing the hissing sound.

Check all vacuum hoses going to the controls, everything other than the fan is vacuum controlled.

Can you tell me exactly where these vacuum hoses are? I took the switch panel out and vacuum hoses are exactly what i looked for and could not find any.

And there was no vacuum lines hooked up the the blending controls?