where exactly does the air get in to the system... I just replaced the hood seal and air is still blowing thru the center floor vents...I could feel cool air coming in on the right fender last night.. I ordered a new seal for that.. but how does the air get into those center vents.. as soon as the car warmed up it was blowing hot air in the center..

 

Outside air enters the C3 cars via a vacuum-operated door (flapper) which is located on the right front fender just before the windshield (wiper-well area). When the car is not running, that flapper should be closed, preventing [supposedly] leaves/etc. from getting into the heater/A-C plenum. Then, the various ducts and flapper doors direct the incoming air, as necessary, through the heater, A/C evaporator coil, defrost ducts, and so on.

The heater controls are vacuum operated and the doors are part of that system. If the vacuum supply, heater control head, damper servos, etc. are not in working order, all sorts of weird stuff can happen within that system. The seal on the right kickpanel vent door is one that usually is almost gone by this time (if it hasn't been replaced). You can repair it yourself for 'peanuts'. Buy one sheet of black, "craft foam" at a local hobby/craft store [Michael's or Hobby Lobby] for about $1 and cut out a new seal with scissors. Make sure you enlarge what you have left, so it will seal well, again. Drill out the rivets on the door pieces to get it apart; use Pop-Rivets to put it back together. Piece of cake!!

P.S. The best circuit diagram and detailed info on the heater control system and servos can be found in the Chevrolet Chassis Service Manual for your model year.

 

the door/flapper that sits behind the kick panel on the passenger side foot well ? or is there another one?

 

There's another one it's in the wiper cowl area, right side, there should be a vacuum hose going to it.

 

I found it.. i put vacuum on it and it opens an closes like it should.... i put a light in the foot well area and could see light coming thru in that area........ so if all the air coming in to the system comes thru that flapper as a test couldn't i block that area with a towel or 2 and go for a ride to see if the air stops? i know its gotta be a seal but just want to see if it will stop,,,

 

You might want to check down in there for STUFF that has gotten past the screen in the cowl area. Some acorns ( that's what was in mine) and other items might just be blocking the flapper from closing all the way. It's scary down there.

 

ohh yeah... i sucked up all kinds of stuff!!! air is still leaking in when the cars moving...

 

I can clearly see the flap is about a 1/2" from closing flat on one side..theres nothing holding it... has anyone got a pic of that area?

 

Once you disconnect the actuator link from that kickpanel door, all you have to do is pull UPWARD on the pivot pin at the top of the door. It is spring-loaded and you can then remove the door.

Drill out the rivets (carefully...JUST the rivets, please), buy the craft foam I mentioned in your other post, cut the seal large enough to do the job [fit it to the opening...not the door], clean/paint as you please, and use Pop-Rivets to reassemble.

You know the door needs to be fixed. Just fix it. Then you can test if you need to do anything else [or not].