I have a buddy who got an 85 El Camino a few weeks ago, the AC system was not working when he got it, I have it working now except the air blows out of the defroster vent and heater vents on all positions: air vent, heat or defrost. The AC blows ice cold air and the heater will cook you. There are 2 vacuum actuators, one on the heater vent outlet, and one for the defroster vent, these both work, the hot and cold selector which is cable operated works also. So everything works except it all blows out of the defroster and heater vents.
I am beating my head on the wall, I don't know what else to check. Has anybody had this kind of problem? Please help, my head hurts.:(

Thanks for any and all help, Kevin.

if the engine is producing enough vacuum, then it might be a problem with the vacuum switch on the control lever.

That is the default operation, so you'll always have defrost. As stated above, it's got vacuum problems. The vacuum comes to the ball on the A/C housing from a fitting behind the carb on the manifold and from the ball into the cabin, check the underhood supply first.

It has good vacuum, 14" at both of the actuator lines inside the car, and both actuators work, I can feel the rods move on them, this is why I can't figure out why it only blows out of the defroster and heater vents.

Is there any place on the web that would have a phantom view of the AC and heater ductwork and the doors that control what vents the air comes out on this year El Camino??

WIDE N LOW,

If the setup is similar to 1970-to early eighties, there should be one more vacuum actuator located behind the heater / defrost housing. It has two vacuum lines going to it and controls the airflow to upper plenum ( defrost/vent) or lower plenum ( heater outlets). If the diaphram is ruptured in this vacuum servo, system will still hold vaccum since vacuum can be applied to either side of the diaphram. Just a thought.

John

I will take another look today, but I think it just has the 2 actuators. I'm not a small person 6' 2'', 300lbs, so crawling under the dash in this thing is a real treat.

check the hard vaccum line under the hood. It goes from under the dash to the vaccum canister. The line usually gets brittle and breaks. It is on the passenger side along the firewall to the inner fender!

I figured it out, the ac/heater control panel has 2 vacuum selector switches, one is a 2 port the other is a 9 port and form some reason both of these vacuum switches leak on the AC mode position, this is the only position they leak on. This is a piss poor set-up, if you have ever seen one.

Same thing on a Monte Carlo of that vintage.

These switches usually don't leak on just one position. the 2 port switch is the heater control valve switch if the valve is disconnected ir bad that switch will loose vacuum when that switch is activated the recirculation door is activated. If that line is leaking or disconnected you will loose vaccum

I wont say for sure in your application. You found the problem it looks like. However, it was mentioned that defrost is the default position, which means if you had only defrost and nothing else. That is evidence that the supply line is the issue. But since your getting air in floor and defrost modes, I would say the chances of a good supply of vacuum from the engine would not be the culprit.

I was going to suggest pulling the control out and seeing if the vacuum "manifold" is connected or damaged. These vacuum lines have a digram in a manual just like a wiring diagram. But they are rarely a fun repair. Laying on your back looking under a dash is almost the worst expierence ever when working on cars.

Ive always wondered. When did GM go from cable operated controls to a vacuum? were all pre 72 Chevelles cable operated.

Well, I misspoke, the defrost and floor are the default operationing conditions.