My 85 IROC-Z blower fan only blows air out the top dash defroster vents. Switching the control to A/C max, bi-level, heater does nothing. Any ideas on what and where to check? Thanks, Badman

Broken vac. line. Look on intake manifold for hard thin vac line. It will be the broken one

Default when a vac problem arises. This is a common thirdgen problem. A search will provide a ton of info.

JamesC

What search words would suggest. I find all kinds of engine vacumn leak info but none a/c blower specific. Thanks, Badman

If the main vac line in engine compartment is ok also inspect the vac lines to the vent selector control on the back side of the control head i ran into an issue where the diaphram was leaking on mine.

Try "defrost and vent". FlaT's suggestion is a good one.

JamesC

Thanks fellows, i'll try those things. Thanks< Badman

My problem turned out to be the vacumn divirter valve located on the a/c controler in the dash. It was broken and causing a vacumn leak.Found one at the Chevy dealer and replaced it. Now I control where I want air blowing out of. Badman