My A/C actually works but no matter what setting you have it on, the air only blows under the dash. I had heard something about a vacuum actuator going bad.

Anyone have an idea what's going wrong and how to fix it?

Thank you!

 

Ah, yet another common problem with the 77-90 B-body cars.

The HVAC system uses vacuum operated doors in the under-dash ducting to direct the air. If vacuum is lost, the doors default to the heat and defrost vents. Start by verifying that the vacuum hoses are connected correctly. My 86 had been completely hosed up (pun definitely intended) by the previous owner. If correct routing doesn't fix the problem, you need to start checking the actuators and the valve. Start with the selector valve on the A/C control head. On my 86 you could hear hissing at certain positions that corresponded to times when the doors did not work properly. If the control head works, you need to use a vacuum gauge and check for vacuum at the actuators in each of the different control positions. If that's good, then check the actuators by attaching and removing the hose on each (when vacuum is applied) to see if the actuator moves.

 

And the 91 and 92 wagons as well.....thought by this time GM would have realized that loss of AC air thru vents also occurs during moderate/heavy acceleration. My 84 did this, my 1st 92 C Cruiser as well, and the one I have now.

 

Hmmm...sounds like another all day project..LOL The guy I bought it from tried to fix it but he didn't know much about cars. When I move the lever on the controller I don't hear any hissing at all and it doesn't even sound like its even attempting to switch modes. Where are the vacuum lines that I need to check?

Thanks for all your help! Wish you were my neighbor Joe...I'd be buying you a lot of lunches...LOL

 

Under the dash in a very difficult to reach place. You will definitely be lying on your back with your feet in the air running this problem down. Of course, you could also completely disassemble the dash to access the air plenum. Good luck!

 

Actually, it shouldn't. There is a check valve in the line that feeds the vacuum reservoir for the HVAC that should keep the vacuum level up even during WOT. My 84 works correctly even during WOT operation of the pavement-ripping 307. Now, my 86 will not maintain proper HVAC operation during WOT, but there is a known leak in the selector valve (I can hear the hissing) so I'm not surprised.

 

I finally got around to checking this problem out. Vacuum tested all the lines in the engine...all were ok. So then I started looking behind the dash...I found out it was the actual controller itself. That black disk that rotates in front of the vacuum lines was broken and it wasn't switching the settings. This happened on my Toronado as well, but there is a little white clip that holds it in place and I was able to super glue it back in. No such luck this time. I was able to order a brand new module for less than $50 from AC Delco...so I'll just replace it.

I'm so happy...course now I have to convert my system to 134A...I think my charge ran out

Has anyone used the Freeze 12? I saw it advertised and it says it's compatible with R12...wasn't sure how well it worked though.

 

I had a 90 Buick Estate Wagon that I converted to R134a. It worked just fine.

 

Yeah I hear the conversion works well if done correctly. My friend is a diesel mechanic and does tons of A/C work. He gave me detailed instructions on how to clean everything out. Only problem is you need a vacuum pump. He also said I could get a hold of some Freeze 12 and recharge with that since it's compatible with R12, no conversion needed. But the system has to be leak free or it can destroy everything when it gets empty...I guess it leaks differently and all the oil goes first so the compressor dries out.