Topic: Cannot change air flow location
in Forum: C3 Cooling and Heating Systems
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Can someone please advise me on what to check. I cannot change where the air flows from. it just comes out the floor. cannot put in on the defrost vents or the dash vents. Don't know what to look for.
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Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
You have a vacuum leak somewhere. It's possible the Climate Control control valve in the console has dried out, and is leaking vacuum from there, but the leak could be in any of the vacuum lines for the HVAC system.You'll need to remove the center console covers to get at the control switch....that's where I would start looking.
I think someone here posted a HVAC system vacuum diagram for the later cars...might be worth a search to see.
I think someone here posted a HVAC system vacuum diagram for the later cars...might be worth a search to see.
Joel Adams
C3VR Lifetime Member #56 
My Link 
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
I agree with Joel. During the annual Gathering last year we had a seminars and Q & A at Bair's Corvettes. The HVAC control switch in the center console is usually the culprit.
I had the same issue with my '81. I decided to replace all my vacuum lines and use a hand vacuum pump to test all the vacuum actuators that open and close the blend doors. It turned out the the problem was indeed the control switch in the center console.
Cheap fix, but kind of a pain to get to. Anytime I have to access the center console I just yank the seats out of the way. Removing those carpeted side panels are a pain with the seats in.
Here is a pic from Bair's website on that Heater/AC Vacuum Control switch Part #IN485 Click on this link> http://www.bairs.com/page216.asp
TKO500 5 spd.
Borgeson Steering Box
Born 8/1981
Sequence #3975
Click here to see more pics of my Vette on CarDomain.
Lifetime Member #26
Lifetime MemberModerator
Duncanville, TX - USA
Joined: 11/8/2003
Posts: 20214
Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
Am-Fm/map light National/Regional/Chapter NCRS "Top Flight"
#2-1985 Bright Red/Carmine Cp.L-98/auto
Member: NCRS, NCRS Texas, Corvette Legends of Texas
Ed...I have the diagram for an '82 I am sending you right now. I'll dig a little deeper into my archives and see if I can find one for an '81. Don't know if the two years used the same system, vacuum-wise, or not. 
Found it...sent it to you also.
|UPDATED|2/17/2016 8:23:23 PM (AZT)|/UPDATED|
Found it...sent it to you also.
|UPDATED|2/17/2016 8:23:23 PM (AZT)|/UPDATED|
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
'81-'82's are the same Joel.
I was looking for my diagram but you beat me to it.
Vacuum hose diagram '77-'82 http://www.docrebuild.com/dr-r-pics/9222-108.GIF
|UPDATED|2/17/2016 8:26:26 PM (AZT)|/UPDATED|
TKO500 5 spd.
Borgeson Steering Box
Born 8/1981
Sequence #3975
Click here to see more pics of my Vette on CarDomain.
Lifetime Member #26
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Milwaukie, OR - USA
Joined: 10/19/2015
Posts: 71
Vette(s): '78 Silver Anniversary T Top coupe,58k orig miles.
THM350 auto, 350 L48, JBM headers,Oyster White interior,.as of Nov '15 in process of painting.
ED.. there are 6 phillips heads screws that hold the glove box interior in..and a bulb-socket.remove the 6 screws with a short phillips head screwdriver..two top front, two bottom front and one each side..remove lamp and wiggle remove the socket toward the cabin interior..then pull the glove box interior liner out..No need to fiddle with latch or hinges on box ..
Once you get the glove box liner out..look back behind atop the ductwork and you will see the bypass vac-solenoid mechanism.
.The control cable on the bypass is coming from the hvac blower climate control console apparatus and is attached to THAT bypass..
The cable does several things..IT'S the mech.temp selector connection from the hvac console unit..and ALSO closes/opens the vac lines that lead to the heater hose underhood vac on off switch solenoid to shut off hot water from heater line and open defroster vent, A/C vent etc. LOOK AT THAT BYPASS switch and operate the temp control lever and SEE IF the cable is adjusted properly to CLOSE it and shut off heated water and open vac to vents..
IF it isn't adjusted properly.you need to remove the pass side console cover and use the turnbuckle on the temp control cable to get the adjustment right..
IS YOUR BLOWER WORKING?
IF it is do the above checkout BEFORE YOU REPLACE THE UNDER Console vac connections..jim
here's the colored link showing what does what..
Former Member
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Milwaukie, OR - USA
Joined: 10/19/2015
Posts: 71
Vette(s): '78 Silver Anniversary T Top coupe,58k orig miles.
THM350 auto, 350 L48, JBM headers,Oyster White interior,.as of Nov '15 in process of painting.
Sarge81 said:
Also read this and check that fitting/nipple Click >http://www.docrebuild.com/dr-r-web/tip3.html
'81-'82's are the same Joel.
I was looking for my diagram but you beat me to it.
Vacuum hose diagram '77-'82 http://www.docrebuild.com/dr-r-pics/9222-108.GIF
Doc Rebuilds diagrams are pretty accurate..but the one I linked to is much better!!IN addition knowing HOW to simply access the vac solenoids/switches for dampers is not readily published anywhere..Jim
in Forum: C3 Cooling and Heating Systems
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