A quick recap...

I've been having problems with my A/C-heater controls, mainly air not coming out of the correct vents. I have been hearing a vacuum leak at the vacuum selector switch and after my last post on the subject suspected it was the rubber vacuum tube manifold not sealing correctly. I got a new vacuum harness and cut off the manifold and spliced it onto the old harness (I didn't want to take apart the dash to replace the entire harness), but I was still getting a vaccum leak. I then got a new vacuum selector switch and that seems to have solved the problem. I would have replaced it sooner but I had already done so about 6 months ago, I guess I got a bad one from the dealer.

Now a new problem has surfaced. No matter what position I set the controls to, I get air coming out of the dash vents. My Helms shop manual shows that no air should be coming out of the dash vents when it is set to off, heater, or defrost. My guess is that the "upper mode" air door and/or vacuum actuator is stuck open and always letting air go to the dash vents. Of course the shop manual shows that the entire dash must be removed to replace that particular actuator. Does anyone know if I can get to it without removing the entire dash or have any other suggestions? IIRC, the door opens when vacuum is applied so it can't be because of a vacuum leak.

 

Dana,

I've always removed, cleaned, and re-greased the vacuum selector switches when I've had such a problem. Since the unit has to be removed anyway, there is little additional labor. A fresh packing with silicone grease generally solves the leakage problems.

As far as the upper outlet air door, you must at least remove the upper dash pad (cover) to access the vacuum actuator and linkage. The "entire dash" doesn't necessarily have to be removed, and removing the upper pad really isn't that difficult.

------------------
Later,
Vader
------------------
"No matter how hard you try you can't stop us now"
Adobe Acrobat Reader 4.0

 

Vader,

Is the vacuum selector switch greased from the factory? How would you grease it? I mean from what I can tell it doesn't come apart. It looks like there are little spaces between the two halves where you could pack some grease into. Is that what you are talking about? Is there anywhere on the switch that I should not put grease?

I did remove my dash pad (I agree, it was a breeze to remove) just to see what I could see, and I couldn't see the upper mode air door or actuator. I take it I would need to remove some of the ducting to get to it? Before I go do this, I need to make sure we are talking about the same thing. There is a lower mode actuator that controls air to the lower vents, and an upper mode actuator that controls air to the dash vents. There is also a defroster actuator and another that controls fresh air intake or recirculating air. I'm thinking it's the upper mode actuator, does that sound correct?
Thanks.

 

bttt

 

When this new problem surfaced, did it occur as soon as you "fixed" your original problem? Reason I ask is because is it possible you put that switch in upside down? If it's installed correctly, the switch only cycles on the top half, so to speak. If it's upside down, the opposing side probably won't control much of anything.

KAM

 

I guess I shouldn't have said that the problem surfaced after installing the new switch. It might have done it before, it's just really noticeable now that the switch is functioning correctly.
The switch is installed correctly, I made sure when I put it in. I actually thought what you mentioned might have been the case with the one I installed previously, but when I took it out it had been installed correctly. The switch has some marks for each position that it rotates to, and I made sure that is how it got installed.

 

I'm assuming you've already done this, but check the vacuum line from your engine that leads into the firewall. It may have a leak, or the bulkhead at the firewall may be cracked. My mom's car has had the selector crap out twice now, and both times, it was the vacuum line from the engine compartment leaking. Hers is plastic where it runs past the battery, and it got eaten through. I just replaced the plastic crap with good old rubber vacuum line and rerouted it away from the battery.



------------------
89RS w/350 TPI; 69RS/SS w/450 HP 350/Muncie 4-Speed "Too weird to live, too rare to die."

 

The parts man at my local GM dealership told me to pull the harness from the rear of the controls (my problem was the same) and swab the black plastic tubes that insert into the harness with Vaseline. I did. Much to my surprise, his fix worked, and after many months of annoyance, I'm a happy camper.

JamesC

------------------

 

Thanks for all of the advice, guys. I ran into a bit of good luck last night. I was reading my Helms shop manual again and looking over the diagram that shows which air doors direct air to which vents. After really looking things over I figured out that it must be the lower-mode vacuum actuator that is stuck open, and not the upper-mode vacuum actuator as I had previously thought. The lucky part is that the lower-mode actuator is the easiest one to get to, you can see it just by looking under the dash. I'm gonna get a new one and swap it in this weekend and hop that it fixes it.