Have a 68 442 4 speed, all original except a really good repaint about 10 years ago. Has 103,000 miles but spent a lot of time garaged.



The car is mechanically sound and runs great. But the factory AC does not work. Compressor runs, though if I turn it on with the selector lever, it kicks in; but when I move the selector back to off, the compressor does not turn off. So I have pulled the power connector from the clutch. The real problem is that the blower fan will run, but no matter where the selector is, all the air comes out the floor vent. So first I gotta fix that. I assume it is a vacuum supply or vacuum control problem, but I have not found an easy way to get to the back of the AC control unit. I have not found any cracked or loose vacuum lines.

I just tested the output of the underhood vacuum canister, and the canister output line to the interior builds to at least 20 inches. The canister when shaken sounds like it has sand or something in it. I was hoping the canister was bad, as that is an easy fix.

I would bet somebody has dealt with this before, and of course knows more about this than I do. My first car in 1974 was a well used 68 Cutlass S, but it had no AC..........

Thank you in advance for any helpful tips!

Chris

 

Page 1C-12 in your 1968 Chassis Service Manual, Figure 1C-22. This is the vacuum hose routing. Verify yours is correct and that you have vacuum at the actuators on the HVAC box under the dash when you're supposed to. Unfortunately, the actuator that operates the MODE door (switching between floor and dash) is the one between the HVAC box and firewall, directly above the trans tunnel. The actuator on the end of the HVAC box, near the accelerator pedal, is the one for DEFROST.

 

That is the way the 70 and earlier systems are from the factory - the compressor clutch stays energized until the ignition is turned off. Used to really bug me back in high school/college when I had a 70 Supreme so I wired in a toggle switch to shut the compressor off.

 

sorry to hijack a thread but I just picked up a '70 cutlass and noticed mine does the same thing. I thought the compressor relay was sticking. This is seriously how they came from the factory? Isn't it bad for the a/c system to be running without the blower pulling air through the evap core? It'll freeze up otherwise.

If this is the case (the compressor staying on after the selector control is turned to off) you could always wire in a reverse momentary switch (normally closed) that'll break the current to the a/c relay when depressed thus killing the compressor until you turn the a/c back on.

Why would GM design the system to work like that? Just curious.

 

Thanks for the quick response & info. I have the service manual, now I get to see how much line routing I can get to without major disassembly......


Re Fun71's reply, I did suspect that the compressor on until ignition off was factory, and I have had a couple of cars that I installed a manual compressor clutch switch into. That is low priority that will need to wait until I get this vacuum door problem solved.


I am trying to avoid removing a lot to get into it, but that may be a lost cause. It could easily be a split/broken/fallen off vacuum line, if I am lucky.


thanks,


Chris