Vacuum for A/C Heater ?

[Lt4-turbo]

My air on my 86 Gn blows cold but it blows thru the defrost vents instead of the A/C vents. I took it in to have it checked out. The Vacuum canister had been removed at some point so my Mechanic replaced the Vacuum canister(ball). It still does not work. He said there was a vacuum switch inside the dash that needs to be replaced but that he couldn't find the part. He said That If I could find the part I should be able to replace it myself.
Does this sound right? I have taken the heat and A/C control out before and I don't remember any switch. If there is a switch where can I find one? Thanks, Jon

 

[scottyb]

First verify that you have vacuum at the control head. There's a series of colored vac lines with a connector behind the glove box door. I *think* the vac source line is purple. Anyway, these lines lead to a round vacuum switch on the back of the control head. If this switch is old and crusty, then it may allow leaks and the other AC vac items won't work. The switch is ~15 or 20 clams at the dealer. I'm a cheap ass - I took mine apart, cleaned it, lubed it lightly with petroleum jelly, and it works like new.

Also make sure that the vac line going back out to the heater control valve is connected. Mine came loose, and the resulting vac leak was enough to cause the vents not to work right.

 

[Lt4-turbo]

Ok I took all the vacuum lines off the control head. I put my finger on all the lines and I don't feel any vacuum on any of them.
What should I do now?

 

[scottyb]

Two of those lines go out to under the hood/firewall. One line goes to the vac source, the other goes to the heater control valve. Follow the onw to the vac source to verify vacuum. It should run (coming to the outside from inside) from the passenger side of the firewall to a check valve over/behind the driver side valve cover. It shares the same vac source with the cruise control and the EGR solenoid. Hopefully you'll find a broken or disconnected line, or a bad/incorrectly installed check valve along the way.

 

[fitz3820]

You can buy a new vacuum ball from GM Parts Direct and also the vacuum switch that attaches to the HVAC control lever in the dash.

Both are fairly cheap, your local GM dealer should have them.

Do a search on the subject to get the part numbers. That is where I got them.

As others have said, check the vacuum lines as they split easily after 17 years of service! One of the hard lines on my car split back near the coil pack under the hood.

 

[Lt4-turbo]

I found a broken vacuum line and I fixed it but it is still not working. Where is the vacuum ball located? My mechanic said he replaced it but I can't find it. I wonder if he really replaced it. He charged me $11 for the ball and $75 labor and I can't tell that he did anything. Thanks, Jon

 

[scottyb]

The ball is under the driver side inner fender. There's a T (or Y) connector for it right by the cruise actuator. For testing, I'd plug the line leading to the cruise, and make sure the check valves are oriented properly.