I got the 72 AC working again. Now for the finer points. I done some googling today and I’m still sort of confused. The actuator located in the passenger kick panel does what? It is my understanding that the recirculation actuator according to the manual is in outside under the right front fender and you get to it by removing the wiper door. When it’s in recirculation mode it should be open or closed. Some guidance and info would be helpful on this

ive added a c-4 blower motor and really didn’t notice a big difference in air flow. The duct are sealed good as I took care when I did the heater core. The AC is blowing cold but it would be easier to cool cabin air than 100 degree outside air. Thanks again

 

When AC is High/Recirculate outside door closes (prevents outside air from entering the fan) and the inside door opens (allows fan to pull in and recirculate cabin air).
See diagram for more detail

 

Well I have that same diagram. From what it looks like is that both actuators run off the same vacuum source and have vacuum applied at the same time to that the doors close when in recirculation. If I remember from a test in the past the actuator in the kick panel it didn’t seem to work so I’ll test it again tomorrow. If one doesn’t work how do it affect the other.

 

On my 73 with factory air, there is a vacuum activate door located in the passenger side wiper trough. Most of the time, it seems these doors are not functional, because they are not easy to see. It’s strange, but the door closes once I start the engine, and the vacuum is brought up. I am sure there is a leak in my vacuum system, but once the engine starts, all the vacuum operated devices work ok.

 

With no vacuum signal the plenum door is normally open and the re-circulation door is normally closed.
Send a vacuum signal to each both change state. Vacuum signal off the line exhausts and they both spring return to their normal state.
Test each actuator separately, each should hold a vacuum and only require 5-6" of vacuum to operate correctly.

 

If your door in the kick panel is not working it could be that the door itself is stuck. Mine was and the vacuum actuator could not open it. My actuator worked fine when I took it off and tested it. Through the years the rust and crud had frozen the lower pivot point enough to cause the door to stick. Took it out and cleaned it up and works perfect now.

 

My '72 vert don't need outside air for HVAC blower......so a removed the inside and outside flapper doors and sealed the outside door closed by disabling a spring on it.....reached through the blower motor hole and cut/removed some of the fender liner and screwed it back in place with fasteners.....

as for not enough force with the C4 blower, check that you getting plenty of voltage to the motor on high speed.....maybe the high speed relay on top of evap housing is no good??? wiring?? and while you got that motor out to block off the fresh air door under the fender, get a nice flex hose from a powerful shop vac and down into the evap housing down LO, where all the annoying leaves/crap from road has been sucked into the fresh air intake, instead of the kick panel....and plugged up the evap coil.....I got about 4" of crap outta mine, many years ago, about doubled the air flow.....

 

I’m going to have a go at the Recirc system tomorrow morning. Can you get to the flapper door on the outside (not the kick panel flapper) by going through the egg crate opening? Also where does the vacuum hose run. Is it easy to get to from the outside so I can hook a vacuum pump to it to check operation? Thank you.

 

You access the outside vacuum door by removing it from the wiper trough. There should be a small vacuum line running into the wiper trough from the firewall. Try searching for a illustration of the vent to see where its located. After refurbishing the rubber seal, I installed it the wrong way. The door is open when there is no, or the loss of vacuum.

 

I am thinking after test this morning that both doors work. I’m thinking it’s a lack of vacuum issue. The kick panel door will open at 8lbs of vacuum and stay open with 5. The line when the motor is running has about 5 in it. I can move the kick panel actuator by hand so it’s not stuck. The headlights and wiper door work excellent BTW

I was checking vacuum lines under the hood and one doesn’t seem to have vacuum. The port it’s connected to doesn’t suck. Even with throttle. I’m going to temporarily move it to see if that has any effect.

However on the way home from my shop the AC sounded different and when I turned it to normal air instead of Recirculation I could hear a difference so I turned it back to recirculation and it was a little noisier, then when I turned the car off I heard a door close Under the dash. Maybe putting more suction In the system with the pump freed something up.

I did a test last night and when it was 108 air temp outside I drove through town and then at highway speed and I was getting between 58 and 64 air out the vents. I’m going to have a really good ac dude double check the Freon levels just to make sure and then put clear heat reduction film
on the windows. Sorry for the rambling post

I’ve had this car since 1975 basically and I’ve decided I’m going to use it as my daily driver so I’m getting the creature comforts up to date.

 

After reading this thread... it now makes more sense to me how the doors work together.

Basically outside air intake is blocked and inside cabin air door is opened to allow recirc.

Now I have to check mine again to make sure it's working properly... I know the outside door is working, not sure about the
one in the kick panel, but it should be easy enough to check.

Thanks for the great thread.

mardyn

 

I’m going to take the counsole cover off and see if I can find a way to check the operation of both doors at once. It appears that the same line feeds both doors. I used my IR temp gun and the kick panel
door showed a temp of 91 while the floor was 80. That was eye opening.

 

All the vacuum activated doors ie, defrost, floor duct, dash vents, outside air door, and kick panel door, are controlled by the selector wheel that turns a vacuum switch. If your vacuum switch/selector has failed, then it would explain why one of the actuators are not working correctly. Willcox has schematics showing the entire system vacuum lines and actuators. Please note that the vacuum lines connections are NOT the same on every C3 Corvette. On my 73, Chevrolet decided not to include a valve to turn off the hot water going to the heater core, even when you have the AC on. Most owners install a manual valve, or a vacuum activated valve, to stop the hot water going to the heater core. You can also find the HVAC Vacuum schematic in the Service Manual. Hope this helps.

 

I’ve got all of that I’m going to check vacuum at the control. All the other stuff work. Heat defrost and vent. I’m hoping to pull
vacuum at the control on the recirculation part and recirculation then works and I’ll replace the control

 

How far is the door in the kick panel supposed to open?

Mine appears only open about 1" from the closed position... I was expecting significantly more movement
than what I'm seeing...

That could possibly explain the low air volume I'm getting through the system.

mardyn

 

That seems about right. You can reach a finger and move the actuator arm and see how much it will open at full pull.

 

Is the rubber material that covers the “flapper door” in good condition? On my car both of them the rubber gasket were falling off. If you need to replace the rubber material, let me know and I will look for the instructions.


You can see that the rubber seal is gone from the edge of the flapper on mine.

 

Just for grins...

I disconnected the return spring and rotated the door to the full open position... I kinda' wedged it
against the kick panel grates to keep it open. It is now about three inches from the closed position.

Didn't make much difference in airflow through the vents, but I'll leave it that way for the moment and try it out on my next
ride.

Edit/Update: Had to move the car around a bit this morning and I think there may be more air volume coming through the vents
after opening the cabin air door to maximum... unscientific observation, but it just seemed to be a stronger breeze coming from the vents today.

mardyn

 

Well I’ve narrowed my issue down. Today I pulled the wiper grill off and I could see the actuator. I decided to cut the vacuum line running to it. I hooked up my vacuum pump to the line with a “t”. Couldn’t pull a vacuum. Ok. I then hooked the vacuum gauge up to the cut side of the line from the control. Started car and saw good vacuum and then I checked the actuator in the kick panel. It had opened!!!!!!! So that tells me that side is working correctly. I then hooked up the pump to the side of the cut line that goes to actuator in the cowl. Wouldn’t pull vacuum. I’m thinking that it’s bad. I did see another post from 2008 that the author found a leaky hose. Can I get that lucky? I’m about to fall out. I’m going to take the wiper door off after it cools outside I’m think just 4 bolts and it should be off. Planning ahead where is a good source for this actuator? Wilcox didn’t think he had them. Are they available?

UPDATE UPDATE😀😀
I’m going to buy a lotto ticket. I went out and got a long screwdriver and moved the hose a little. It had go up against the wiper post and looked funny. It had a hole !!!!! Stopped for night. I’m going to take the easy way out and cut it and put a t or connector in the bad place to see if it works. Then fix properly when it cools off in the fall.

 

https://www.zip-corvette.com/69-81-a...-actuator.html

https://www.zip-corvette.com/69-82-r...door-only.html