i've got an odd problem with my HVAC. if i have the switch set to ac, bi-lev, vent, heater, or defrost the air only blows through the defrost vent under the windshield. the only way to get air to come through the other vents is to set it to max ac. sometimes if i run it on max ac for 5 minutes then change to vent or heat it will continue to come from the vents. anyone know what's goin on?

 

Check the vacuum diaphram just above and to the right of the gas pedel under the dash. You will see a vacuum line with a clear elbow plugged into it. This changes your air door setting. Is the vacuum line still plugged in?
Its posible to kick it loose. If not, Can you hear a hissing noise from under the dash with the engine running? (vacuum leak)

 

second that! It's a vac leak that causes it to get stuck on defrost. Had that in my '88 RS, was a pain to find the leak, had to tear the entire dash out to find the nice little mouse nest. HVAC hoses all intertwined and chewed within the nest, lol. Good luck!

 

Stick an ear to the HAVC head. Should you hear a hiss, your problem probaby stems from the vac control valve:

https://www.thirdgen.org/forums/atta...duct010707.jpg

https://www.thirdgen.org/forums/inte...ctor-disc.html

By the way, this problem is common to thirdgens, so a search will provide pages of info.

JamesC

 

thanks for the info guys