68 vacuum operated vent valve

[Lloyd A. Kilpack]

What does this connect to ? I have a 68 airconditioned car. Behind the kick panel and just in front of the speaker there is a vacuum operated valve. It appears to be part number 3917319. It operates nothing. There is no door attached, nor is there a cable attached. The valve appears to be in good working condition as it holds vacuum. The small compartment that is in back of it goes nowhere. It appears to do absolutely nothing. Is this because I have an airconditioned car? Many thanks in advance for any ideas as to what this is supposed to do. Also, my assembly manual does not describe this valve. It only shows manual cables attached to wheels on the shifter plate. I do not have those, I am assuming because the car has air.
Lloyd Kilpack member #31688

[Terry M.]

Re: 68 vacuum operated vent valve

Lloyd,
I believe that is the valve which controls the air going into the heater/cooler chamber. It directs either inside or outside air through the HVAC plenum. I think you will find that part in the C60 (air conditioning) section of the AIM - in the back of the book with all the other options listed alphabetically.

[Lloyd A. Kilpack]

Re: 68 vacuum operated vent valve

Terry:
Thanks for the direction. I have found what you described on C60 A1. It is a side shroud vacuum control. The problem, as I see it, is that it controls nothing. I do not have a door there as shown, and if there was a door it would lead to a very small sealed compartment in the left front fender. I dont see why or how air would be dirverted into or out of this compartment. Do you think I could be missing the whole door assembly as shown on C60 A4 ? If I am what are the consequences of not replacing it ? I dont think that I have seen this item in any of the parts catalogs that I have.

Thanks Again Lloyd.

[Terry M.]

Re: 68 vacuum operated vent valve *TL*

Lloyd,
Is your car and early production? Maybe built in 1967? If so, the AIM pages may be different than how the car was produced. In general the AIM pages we use are from late in the model year and there may be changes made during production which are not reflected in the version that we use.
Another possibility is that sometime during its life your car was repaired by "Bubba" who failed to install all the parts. I hope the issue is the former. Fixing "Bubba's" work can be very difficult.

[Jim T.]

Re: 68 vacuum operated vent valve

Lloyd what do you have on the passenger side of the car? Is there a vacuum operated door that opens when you select MAX air and closes if anything else is selected? I have a 70 with air and the door opens when MAX air is selected which also closes a plenum access for ambient fresh air under the rear right fender which allows for interior air to be recirculated for MAX cooling. The left side is sealed off on my 70 and no air can enter or leave.
If there is no door on the left side like you mention, what about air, do you have air flow through this area?
I have a 68 without air and both left and right side doors are operated by manual controls on the console and are fuction as a source of air for the astro ventilation system as well as the dash vents.

[John H.]

Re: 68 vacuum operated vent valve

If I recall correctly, there are two vacuum-operated valves involved here, and they work in concert depending on control settings. The valve in the kickpad (which is apparently missing) is normally closed; it only opens when the control is in the "Max" position, and in that mode it admits inside air to the plenum feeding air to the evaporator for maximum cooling. The other valve/door (the plenum valve) is further up (buried under the wiper door and actuator/linkage etc.); it's normally open, and admits outside air to the plenum feeding the evaporator - when "Max" cooling is selected, this door closes (at the same time as the kickpad valve opens), shutting off outside air so only inside air is recirculated through the evaporator.

[Lloyd A. Kilpack]

Re: 68 vacuum operated vent valve

Thanks guys for all of your input. I am afraid that Terry was right and "bubba" has been at my car. As near as I can tell there is a door that is missing. The vacuum operated valve that I described is controlled by the mode set on the wheels. If it is shut it creates MAX air conditioning, and closed, circulates outside air. All need to do now is find a door. Everything else is in place. Thanks again for all of your help.
Lloyd.

[Jim T.]

Re: 68 vacuum operated vent valve

So Lloyd you were not missing a door on the left side like you posted, you are missing the door on the right side/passenger side and your left side should be sealed since your car is an factory air 68. I could give you the part number of this door since I bought one years ago to replace one that the seal had deteriorated on. I don't know if it is still in GM's part system or not. You might be able to get a used one from Contempory Corvettes from a donor car. Are your two mounting pieces still installed. Don't remember exactly, but I think there will be a smooth metal pin at the top and one at the bottom that the door pivots on. A spring on the bottom supports the door up vertically enough to keep it connected to the top pin. Pretty easy to remove and install.
The upper door on the right side that prevents ambient air to enter from the cowl is actually under the top rear of the fender well clear of the windshield wipers and their associated cowl mounted moving and stationary parts.

[Lloyd A. Kilpack]

Re: 68 vacuum operated vent valve

Jim:
Thanks for your reply. Sorry for the confusion. Yes my car is a factory air car. I do not have a door or vent on the drivers side at all. I have the vacuum operated actuator mounted just in front of the speaker and very close to center of the plenium vent on the passenger side. There is no indication that a door was ever there. i.e. mounting bracket, hinges etc. I have been able to locate the routing of the vacuum hoses and figure what is supposed to go where compliments of the AIM and you guys here. I have located the vent door above the plenium vent just under the grille on the passenger side. However, I am missing the door. Bubba strikes again, or perhaps my car was a doner at one time. If you have the part number handy, I would appreciate it.

Thanks Lloyd.

[Jim T.]

Re: 68 vacuum operated vent valve

I was wrong about mounting pins in your car. The mounting pins are part of the door and are permantly mounted to the door/valve assembly to allow installing the valve assembly. One end of the valve assembly will have a spring loaded pin. You should have only a small hole about 1/8 inch at the bottom and top of the valve assembly mounting area that will provide vertical mounting of the valve assembly. The valve assembly is from
GR 9.789 and part number 3940636 and part name is a valve assembly.
Without either one of the valves/doors installed in your 68 a passenger will most likely feel a cool draft in the when the ambient temp is at or near freezing when going down the highway. The lower valve is metal with a seal around the perimeter and the upper valve is made of plastic.

[Jim T.]

Re: 68 vacuum operated vent valve

Think I have found the part number for the plastic seal that closes off ambient air from the cowl area to enter the plenum on the passenger side with your 68 factory air system. The part is identified as a seal and GM #1950569. This was taken from records of a seal bought in the 80's. Don't know if this piece of plastic that is mounted on a steel bracket and is moved by a vacuum relay is still in the GM parts system. The parts tag actually lists the part as 01950569, but I believe the first number is not used.