C3 1969 Air Cond. Vacuum Plenum Valve

[Jimmy B.]

While I was inspecting my cowl area after removing wiper door and arms I noticed a vacuum hose kindof hanging precariously over part of the inside inner fender on the rh side. Curiosity got the best of me so I pulled on the hose and this plenum valve with actuator assembly just came up through the hole. It wasn't screwed to anything. I found it in the AIM so I am sure Jack H. is proud of me. See C60 A4. Curiously I put my vacuum tester (Snap-On) on the actuator and could not get the rod to activate,

1) is there something I am missing here?

2) do I have a bad assembly?

3) what do the screws look like to mount this GM 9419321?

4) what does this thing do?

5) my 1969 Chassis Service Manuel is helpless for air conditioning, is there another GM reference source I need to purchase?

Should I buy Mr. Jack H. an airline ticket and get his Colorado butt out here?

Regards,

Jim Blakely

[Chuck S.]

Re: C3 1969 Air Cond. Vacuum Plenum Valve

2) do I have a bad assembly?

The actuator diaphragm probably has a huge rot hole in it, or there's a big "fringed" hole that used to be the diaphram.

3) what do the screws look like to mount this GM 9419321?

I expect they looked just like the ones used in 70...#8 Sheet Metal screws, 5/8" long, with indented flanged hex heads, and finished black phosphate. Mine had no head stamps.

4) what does this thing do?

This valve seats against a hole in the fiberglass bulkhead that partitions the fresh air plenum from the interior of the car. When the AC controller is moved to MAX or vent, this valve opens allowing fresh air to flow from the front plenum into the AC, or into the car interior through the RH kick panel .

[Joe L.]

Re: C3 1969 Air Cond. Vacuum Plenum Valve

While I was inspecting my cowl area after removing wiper door and arms I noticed a vacuum hose kindof hanging precariously over part of the inside inner fender on the rh side. Curiosity got the best of me so I pulled on the hose and this plenum valve with actuator assembly just came up through the hole. It wasn't screwed to anything. I found it in the AIM so I am sure Jack H. is proud of me. See C60 A4. Curiously I put my vacuum tester (Snap-On) on the actuator and could not get the rod to activate,

1) is there something I am missing here?

2) do I have a bad assembly?

3) what do the screws look like to mount this GM 9419321?

4) what does this thing do?

5) my 1969 Chassis Service Manuel is helpless for air conditioning, is there another GM reference source I need to purchase?

Should I buy Mr. Jack H. an airline ticket and get his Colorado butt out here?

Regards,

Jim Blakely

Jim----

A bad vacuum actuator for this application is a problem. The last available actuator, GM #1996607, was discontinued without supercession in April, 1989. I don't know of a source for a replacement although there may be one.

For a life-limited piece like this I'd be very reluctant to go used unless there was absolutely no other alternative.

[Jim T.]

Re: C3 1969 Air Cond. Vacuum Plenum Valve

Chuck if I understand that Jimmy B. pulled out the plenum valve, this plenum valve closes off fresh air to the air conditioner when you select MAX. When MAX is selected on my 70 this plenum valve closes and kick panel valve opens to recirculate the interior air, no outside air is selected on MAX.
The plenum valve that Jimmy B. pulled out should be somewhat flat looking piece of plastic. There is a small metal brace that is attached with a couple of screws that secures the plastic plenum valve so it can function by commands from the actuator, either open or closed. If the wiper cover and the cowl vent grille are removed it is real easy to look down where the valve is. You can see the fan motors blower real easy when this plenum valve is open, when it closes the fan motor blower is not seen because it will close, moving towards the drivers side. I bought a new plenum plastic valve in in 85 or 86, am sure they are no longer available. Was even able to buy the new metal bracket from GM.

[Jack H.]

Re: C3 1969 Air Cond. Vacuum Plenum Valve

Hard to tell what you're describing from the text, but I'll guess you're talking about one of the two cabin air door vacuum actuators (recirculate vs. vent/exterior). One 'lives' in the RH cowl controlling the source of makeup air that feeds the plenum while it's twin (they form a flip flop) lives behind the RH interior kick panel.

It's a )(*&^ of a job to replace the upper vac actuator because it was intalled prior to the front clip being bonded onto the car! But, those who have 'rate buster' mechanic status CAN get the job done rather quickly....

As Joe mentions, finding an NOS original isn't gong to be easy, but they're readily available used from those who part out Shark cars! If memory serves, I squirreled away spares for my '71 sometime back, but I haven't checked to see where I'd stached them.

[Chuck S.]

Re: C3 1969 Air Cond. Vacuum Plenum Valve

Chuck if I understand that Jimmy B. pulled out the plenum valve, this plenum valve closes off fresh air to the air conditioner when you select MAX. When MAX is selected on my 70 this plenum valve closes and kick panel valve opens to recirculate the interior air, no outside air is selected on MAX.

Yes, you are correct. I remembered the AC operation being somewhat counterintuitive when set to MAX, but I must have been remembering another car.

The plenum valve that Jimmy B. pulled out should be somewhat flat looking piece of plastic. There is a small metal brace that is attached with a couple of screws that secures the plastic plenum valve so it can function by commands from the actuator, either open or closed...

Actually, there are three screws as I described before, plus a pin on the actuator bracket that indexes one corner to perfectly position the valve during the original assembly. Edit: My memory is also a little hazy on this "pin" as well...without getting the valve out to look, I'm thinking that the "pin" may actually be a tiny "double-ended" nipple that is molded into the plastic door...the vac supply line attaches to the plenum end of this tiny nipple. The actuator is actually attached to the fender side of the plastic door with a short connector tube, and swings out into the fender with the valve when actuated.

...I bought a new plenum plastic valve in in 85 or 86, am sure they are no longer available. Was even able to buy the new metal bracket from GM.

And to my knowledge there is no repro...if you need one, you're most likely SOL unless you happen to find one from a part out C60 at Carlisle or on epay.

I remember, once-upon-a-time, that Jerry Clark was restoring one very nice 69 big block car with AC, black. I think. He came on the old TDB one day frantic to find that valve. Well, it just so happened that I had run across one on epay just days before, and had noted the unusualness of seeing one. I found the listing again for Jerry, and he ended up with it...he was one happy camper...for awhile. He later sold the car to a well-known doctor...think of me and Jerry, Doc, if/when you turn on the air.

Jimmy, if you want to understand how the system works, look at the schematic diagrams in the AIM, UPC C60, Sheets E5 and E6...that shows what valves are opened and closed at what settings, and how the air moves through the system.