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Old 04-29-2007, 04:49 PM   #1
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A/C Vents

hey guys i just got a 77 Vette. and i the air from the A/C only comes out through the bottom vents when it is cooling. I know it is a vacuum ordeal but has anybody experienced this so they can lead me in a faster direction! Thanks dudes
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Old 04-29-2007, 10:50 PM   #2
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There is a vacuum actuator for the air door that directs the air to the upper vents. This is a vacuum/electric diagram of a 68 HVAC setup. Your should be very similar. Sounds like a disconnected vacuum line to me (or a bad actuator). You might have to prit this to really see.

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Old 04-29-2007, 11:09 PM   #3
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Thnks alot!
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Old 05-03-2007, 08:13 PM   #4
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There is a vacuum actuator for the air door that directs the air to the upper vents. This is a vacuum/electric diagram of a 68 HVAC setup. Your should be very similar. Sounds like a disconnected vacuum line to me (or a bad actuator). You might have to prit this to really see.



Hi there, I have a similar problem on a 68 coupe if I can ask a quistion here about it? In hooking up the vac. line and looking at this diagram, it shows a actuator in the plunum, yea cool where is that? I took the heater box out and nothing and see nothing in where the cooling air comes in. I see the one actuator in the kick pannel only, is the another one I don't see on my car? And it is a 68 coupe with air. Thanks so much if you can help. Manuel
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Old 05-03-2007, 09:24 PM   #5
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Hi there, I have a similar problem on a 68 coupe if I can ask a quistion here about it? In hooking up the vac. line and looking at this diagram, it shows a actuator in the plunum, yea cool where is that? I took the heater box out and nothing and see nothing in where the cooling air comes in. I see the one actuator in the kick pannel only, is the another one I don't see on my car? And it is a 68 coupe with air. Thanks so much if you can help. Manuel
Manuel, The actuator that is in the plenum is not visible unless the front clip is removed. You may see a vacuum line going down to it from the wiper well. This actuator switches between closed cabin mode (air from inside the car is re-cooled) and fresh air mode where outside air is cooled. The actuator in the kick panel works in conjunction with the plenum actuator. They are both connected into the same line with a T connector. The kick vent is normally closed (by a spring) and the plenum actuator is normally open.

It seems like a complicated system but it all makes sense when you take a look at it.
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Old 05-04-2007, 12:49 AM   #6
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Manuel, The actuator that is in the plenum is not visible unless the front clip is removed. You may see a vacuum line going down to it from the wiper well. This actuator switches between closed cabin mode (air from inside the car is re-cooled) and fresh air mode where outside air is cooled. The actuator in the kick panel works in conjunction with the plenum actuator. They are both connected into the same line with a T connector. The kick vent is normally closed (by a spring) and the plenum actuator is normally open.

It seems like a complicated system but it all makes sense when you take a look at it.


Thank you for the info! The hose is off on my car as it is just going back together after a frame off. But I didn't have the front clip off the body and I don't remeber this hose being attached anywhere. I wanted to be sure I had all the mechincal done before finishing my body work. Is there a way to get to this actuator that you know of without taking the fenders off? Again thanks for the help!! Manuel
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Old 05-04-2007, 01:40 AM   #7
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Thank you for the info! The hose is off on my car as it is just going back together after a frame off. But I didn't have the front clip off the body and I don't remeber this hose being attached anywhere. I wanted to be sure I had all the mechincal done before finishing my body work. Is there a way to get to this actuator that you know of without taking the fenders off? Again thanks for the help!! Manuel
YES, you can look down in there with a flashlight, and you will see 2-3 5/16 hex bolts on a small metal bracket, that door is removeable, , actuator and all...hard to get to....sometimes the rubber sealer material gets awful tired and cracks/falls off....I had the actuator fail some years ago on my '72 here where I had to pull the entire door mechanism to get to it.....I just sealed it all off permanently, and pulled the inner door off, eliminating the vac line....permanent recirc for my car....being as it's a convertible....I got plenty of fresh air.....
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Old 05-21-2007, 05:44 PM   #8
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So when the AC is on MAX, the kick panel door should be open and the plenum door should be closed?

Im getting good air flow out of the side vents, but my upper vents dont have that much flow. They work, there is just not as much air coming through them as the side vents. I have confirmed the kick panel door is open, as it seemd to want to close when I switch to norm, but there doesnt seem to be any change in the amount of air in the center vents when I go from norm to Max,

any ideas?
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Old 05-21-2007, 06:19 PM   #9
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Originally Posted by jotape650 View Post
hey guys i just got a 77 Vette. and i the air from the A/C only comes out through the bottom vents when it is cooling. I know it is a vacuum ordeal but has anybody experienced this so they can lead me in a faster direction! Thanks dudes
Good possibility you have a vacuum leak somewhere in the main feed or early on in the system. When there is no vacuum, the system defaults to the heat position (figures with a car designed in Detroit).

Pull the main feed line under the hood (black nylon line that connects to other rubber vacuum lines on engine side of the firewall) and see if you can hook a hand held vacuum pump to the line and apply a vacuum. If it holds the vacuum on the gauge when you let it sit, the leak is not in the system, rather in the vacuum source.

From there, follow the diagram someone posted and pump, read and repeat until you find the culprit.
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Old 05-21-2007, 07:23 PM   #10
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so this is off topic, somewhat but w.e... my A/C fan only blows air in all the settings except HI. is the switch shot?
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Old 05-21-2007, 07:48 PM   #11
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so this is off topic, somewhat but w.e... my A/C fan only blows air in all the settings except HI. is the switch shot?
Probably not. There's a special in-line high current fuse for the high speed setting on the fan. If I recall correctly, it's a 30A fuse. It's either located on the heater core box or on the firewall (its been a couple of decades since I had to replace one, so forgive the lack of detail!).

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Old 05-22-2007, 09:56 AM   #12
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so this is located somewhere on the passenger side? it isnt going to be on the normal fuse box? thanks alot!
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Old 05-22-2007, 04:36 PM   #13
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location any1?????????????
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Old 05-22-2007, 05:10 PM   #14
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location any1?????????????
On a 79 it would be a fusable link between the starter and the high speed blower relay.
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Old 05-23-2007, 07:17 AM   #15
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well it is extremely similar to the AC relay on the firewall but i found it under the center console underneaththe shifter. some1 had unplugged it and never replaced it!1! thanks everyone
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