1979 Corvette A/C Question
Thread Starter
Melting Slicks
Joined: Aug 2004
Posts: 2,479
Likes: 12
From: New York
1979 Corvette A/C Question
Now that we have the Air Conditioning working in the 79; is the A/C supposed to blow out of the top vents? Or blow out of the bottom of the dash?
Thanks,
-Dave
Thanks,
-Dave
Team Owner
Joined: Jul 2006
Posts: 22,150
Likes: 4,165
From: Kannapolis NC
I'd say the ducts that feed the air up are either disconnected or blocked. I opened up a Toyota dash one time and the vent was totally blocked by a rat's nest. It was full of insulation from the car, drinking straws, paper, lots of junk. Most likely, someone has removed part of the ducting, maybe for stereo clearance. Or maybe they just didn't notice it was loose.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
Race Director
Joined: Apr 1999
Posts: 11,520
Likes: 13
From: CORVETTE 77 385 C.I. TEXAS
I wrote this up awhile back for this problem.
On at least later C3 the problem is that heater is the default position (no vac. or vac. leak) due to being designed in the north. Vent should be default. Very safe bet the problem is 1 OR 2:
1) The vac. line from engine is damaged from heat - a small plastic tube that goes in below the hood alarm switch into wiper valley. Replacing most of engine side w/ hose will fix. OR
2) The vac. switch itself is not switching due to vac. leak as the usually plastic rivet is not holding the 2 main switch parts together well. Besides replacing, it is also possible to tighten this &/or lube w/ a thin layer of white lithium grease or vasoline to fix.
3) If you have a heater, the small vac. tube to heater hose valve underhood probably also needs replacing. Block w/o heater.
PS The design problem comment is not intended to be offensive to any of our northern friends.
On at least later C3 the problem is that heater is the default position (no vac. or vac. leak) due to being designed in the north. Vent should be default. Very safe bet the problem is 1 OR 2:
1) The vac. line from engine is damaged from heat - a small plastic tube that goes in below the hood alarm switch into wiper valley. Replacing most of engine side w/ hose will fix. OR
2) The vac. switch itself is not switching due to vac. leak as the usually plastic rivet is not holding the 2 main switch parts together well. Besides replacing, it is also possible to tighten this &/or lube w/ a thin layer of white lithium grease or vasoline to fix.
3) If you have a heater, the small vac. tube to heater hose valve underhood probably also needs replacing. Block w/o heater.
PS The design problem comment is not intended to be offensive to any of our northern friends.
Team Owner
Joined: Jul 2006
Posts: 22,150
Likes: 4,165
From: Kannapolis NC
Sorry, I mixed up your question with the post by cruise83 about lower vents. If it's coming out by your feet, then it probably is in either the vacuum or actuator that moves the air flow as Ganey says. I thought your cold air was coming out the lower vents (not the heater vents) when I answered.
Cruising
Joined: Mar 2005
Posts: 11
Likes: 1
I would like to know as well
Is there a specific spot to view a diagram of the internal vacuum hoses? My '78 has similar issues. I have no vacuum at the heater hose valve under the hood. So I am working backwards.
Please post info as you get this figured out. Thanks
Please post info as you get this figured out. Thanks
Safety Car
Joined: Oct 2007
Posts: 4,364
Likes: 1,724
From: Seattle Area Washington
Cruising
Joined: Mar 2005
Posts: 11
Likes: 1
Finally info for that pesky air vent not working!
Bmotojoe you are my hero!!
I really appreciate this! Between your diagram and the following one I will share here, I actually found my leak. It was the tiny 1/8" air supply through the firewall, somehow had burned and sealed it's ends near the tee.
I feel that including this diagram for others, that they may find this post in the future...
I really appreciate this! Between your diagram and the following one I will share here, I actually found my leak. It was the tiny 1/8" air supply through the firewall, somehow had burned and sealed it's ends near the tee.
I feel that including this diagram for others, that they may find this post in the future...
Melting Slicks
Joined: Oct 2006
Posts: 2,417
Likes: 336
From: Texas
i just had to fix mine yesterday, the AC air was blowing out the vents on the floor, the three small plastic hoses that exit out the grommet on the fire wall were broken, brittle from engine heat. i was able to remove the glove box and push the hoses through so i could reattach them with some small vacuum tubing. (temporary fix), order new vacuum tubing kit from zip. i believe with no vacuum it defaults to the floor. it could also be the vacuum rotary switch underneath the console ac control panel. i had to replace that also last year. thats a good pic there bmotojo
Instructor
Joined: Jul 2011
Posts: 142
Likes: 1
From: Fort White Florida
I didn't want to start a new thread as the OP's problem is the same as mine. I know it is a vacuum problem. It is too hot out in the garage to work on anything and I wondered if there is anyway to force the air to come out of the dash vents as a temporary fix until it the weather cools off a little.
The vacuum control switch/valve seems to move freely but, rotating it does nothing.
Thanks Rick
The vacuum control switch/valve seems to move freely but, rotating it does nothing.
Thanks Rick
Last edited by Rick_V; Jul 24, 2011 at 03:42 PM. Reason: More info.
Instructor
Joined: Jul 2011
Posts: 142
Likes: 1
From: Fort White Florida
Looking at the schematic from my AIM it looks like only ONE (black hard plastic) of the three lines coming through the firewall goes to manifold vacuum, one goes to the heater water control valve (clear) and the other (green) goes to the passengers side to I believe the bi-level control (not sure don't have the AIM in front of me). Well on mine the small black hard plastic one goes to vacuum but so does the clear one into a "Y" and the green one goes to where it should. Could the fact that the PO hooked this up wrong be the root of my problem?
Advanced
Joined: Jul 2011
Posts: 89
Likes: 0
From: Toledo Ohio
My 79 has the same problem I think. Have vacuum to heater control valve in heater hose. Fan works but vent, heater, def. does not change pos. You should be able to hear the sound of the air when it changes positions. It seems that the air is comming from the floor outlets but not 100% some from def. Any ideas to look for??
Last edited by travelerbob; Oct 26, 2011 at 11:00 PM. Reason: additions
