i have an 86 chevy caprice, 125k, the air blows cold, but its stuck on defrost, the switch activates the air, it just don't switch to vents.......its not the switch..........i had an 85 chev conversion van that did the same thing to me, any help pointing me in the right direction would be greatly appreciated
thanks
cougnut

i have an 86 chevy caprice, 125k, the air blows cold, but its stuck on defrost, the switch activates the air, it just don't switch to vents.......its not the switch..........i had an 85 chev conversion van that did the same thing to me, any help pointing me in the right direction would be greatly appreciated
thanks
cougnut

Check the vacuum lines that attach to the control, and again to all of the dashpots (vacuum motors) and ensure that none of the vent doors are stuck or jammed. When you pull out the glovebox, you'll see the main door cable underneath - make sure it's still on its peg and that the sheath hasn't come loose from the A/C assembly.

Also check under the hood - the "Orb of Nothing" as Blue Bowtie called it once, aka the vacuum reservoir, check it to ensure that none of the vacuum lines attaching it are broken or pulled off. This looks like a black ball about 4" in diameter, attached to the evap coil housing. One of these goes directly to the intake manifold behind the carb, and the other one is one of those hard plastic lines that like to get brittle and break. Check the condition of this latter line to ensure continuity all the way to the firewall - it is this line that supplies vacuum to the controller under the dash, and then to the vacuum motors in turn.

ok, i checked the black orb, lol, that hooks up to the intake, then to the cruise, it all checked out, i'll check behind the glove box to see if the "flap" is stuck or something physical like that.........i'll update you guys, thanks again in advance...........cougnut

no luck, all the vacumm lines are in great shape, a mechanic friend told me there might be a filter for the ac thats clogged, is there any truth to this, or is he full of shi........
thanks
cougnut

He's partially full of sh!t.

Some newer cars have cabin air filters.

No b-body ever came with one though.

Make sure you check the vacuum lines under the dash as well. Also, there is an -oring in the switch itself that controls where to pull the vacuum from. This could have gone south.