a/c- heater dash control unit

[Longroof79]

I've recently had my new a/c installed and charged up. I have noticed that when in a/c mode, the air comes in from the defrost vents and lower vent(s) only, and not from the forward vents.
Do these control units go bad over time?
I did manage to get underneath the dash and connected my vacuum/ bleeder pump to one the two vacuum servos that open and close the flap, or blend door. I started the car and turned the a/c on, and kept the vacuum pump on one of the servos. It did divert the air to the forward vents.

Now I'm assuming it might be the control unit itself, being that it's vacuum controlled or activated.

Has anyone had to replace the dash control in order to have the vents working properly, or is it more likely to be the vacuum line going to it?

Also, are these units used in later GM cars? Perhaps I can find a later unit that's in "fresher" condition.

 

[81Regal]

Jack, I remember seeing some body that had new GM parts to fix your problem. It's the round diaphragm that mounts to the controls, there is a thin piece in there that dries out over time and brakes.
Might try mikesmontes or g body parts.

 

[O. D. Showtime]

Jack I know we had trouble with Cody's Malibu with that part that Jeff is talking about...his got so bad you could here the vacuum leak behind the control. I had another here but we never did swap it out before selling the car.

I'd check the vendors Jeff mentioned for a new one.

 

[Longroof79]

Jeff and Kevin,
Thank you guys for your input and suggestions. I figured I was on the right track. I do have another control I can swap out, or if I can purchase the rubber diaphragm separately, I'd probably rather replace it with a new part. These things do come apart easily once it's removed from the dash.

 

[Longroof79]

These units are NLA. Hopefully, I can put something together picking and choosing the best parts.

btw, Mike's Monte's only sells used control units from what I can see.

 

[liquidh8]

Let us know what you find Jack, I too may have the vacuum part laying around somewhere. I usually check the diaphragms first. just take a piece of vacuum tubing and attach it to the diaphragm, suck and see if it is operating. Rinse and repeat for all three. They are a pain in rear to get too. The control head is easier to try I suppose, but that is only if you have a spare.

 

[Longroof79]

Hey Jim,
Well, I have a spare unit that originally came with the GP dash. I started out by reusing my original Malibu unit. that was easier than unhooking and reattaching everything.
Anyway, I had the fun of replacing it yesterday and started the car and checked for function....same sh*t.It's still blowing out of the defrost vents and lower vents. I made sure both vacuum connections were connected.. I had checked all the servos, sucking on a piece of thin hose . They all seem to work effortlessly. It's got to be a vacuum leak somewhere.
Oh, and also, the end of lower selector cable broke at the end...and also the plastic pivot had broken off. I'm going to make a new inner cable with a piece of thin welding rod..thicker than MIG wire. When I tried it, the vent was in the right position. I might have also felt an air leak under there. I'll see if I can stuff it with foam...or expandable foam. That might not be a good idea....that stuff spreads like crazy.

So, as you see, I'm still at square 1...but I'm open to suggestions. How would I go about testing the diaphragm. Which ends would I have to draw vacuum from? All together from what I can see, there's 3 servos. One at the right end of the dash, and 2-in the center in back of the radio.
Another question...where is the vacuum drawn in from?

Would I have to submerge the diaphragm pod in water, and try the vacuum test, or just squirt some soapy water around it, like trying to find a hole in an inner tube?

 

[Longroof79]

As I figured, the vacuum feed for the control is connected to the round vacuum ball under the hood.
I tested both the purple and the gray lines. The purple is the actual vacuum feed. The gray line goes to the heater valve on the intake. Both lines hold vacuum...no leaks there. I still think the control unit diaphragm is the likely culprit.
I swapped it out the other day and it's acting the same way. I even tested the vacuum ball, that's fine.

When I try pulling vacuum directly from the control unit, you can hear the air escaping. The spare vacuum diaphragms that I have, all seem soft and pliable. I'm at a bit of a quandary with this thing.
The vacuum lines all look good. I may take a visit to the junkyard and see what I can come up with.
I'm guessing some of the later GM cars may use the same, or similar control units. Even if I can cannibalize another unit for parts, I'll be happy.
Another fine product brought to you by GM.... what a piece o' sh*t.

 

[Malibu Bob]

Jack, I remember seeing some body that had new GM parts to fix your problem. It's the round diaphragm that mounts to the controls, there is a thin piece in there that dries out over time and brakes.
Might try mikesmontes or g body parts.

i have a used one, most of time its a vacume problem call Malibu bob 1-317-299-2773 indy

 

[pontiacgp]

Jack, have you tested to see how much vacuum you have?