Annoying AC issue
Thread Starter
Advanced
Joined: Sep 2021
Posts: 88
Likes: 40
Annoying AC issue
My 72 factory AC works well except for one annoying issue. After 10-15 min or so of blowing strong through the center and ball vents the airflow gradually tapers off at the center vents and reverts to floor. I then have it blowing from all three instead if just the center and ball vents.
This is on MAX AC setting on dial which is the only way I run it. I dont believe its a leak at the dial as I checked that closely when I redid the carpet last winter.
What changes from start up when its working correctly?
This is on MAX AC setting on dial which is the only way I run it. I dont believe its a leak at the dial as I checked that closely when I redid the carpet last winter.
What changes from start up when its working correctly?
Race Director
Joined: Oct 2000
Posts: 12,658
Likes: 3,117
From: Shamong, NJ
I'd have to think it's a slow vacuum leak somewhere allowing one of the diverter doors in the heater box to close. I'm just guessing, but it's likely some kind of problem with a vacuum actuator on a door either leaking or having some other kind of problem causing it to close the diverter.
Thread Starter
Advanced
Joined: Sep 2021
Posts: 88
Likes: 40
I also figured a leak at actuator. What I cant understand in my feeble brain is why does it work right off the bat at idle on start up? Its as if theres a big burst of vacuum to operate it initially, but at higher RPMs once I am driving it cant keep up with a leak.
Le Mans Master
Joined: Jun 2019
Posts: 7,649
Likes: 2,466
From: Indiana
it is probably the switch.. here is a great switch thread for many years..skip to post 30 for a 72 example..
https://www.corvetteforum.com/forums...-switch-2.html
https://www.corvetteforum.com/forums...-switch-2.html
Instructor
Joined: Jan 2016
Posts: 226
Likes: 79
From: Boise, Id
Not 100% sure if a 1972 corvette has a vacuum tank of some sort, but if it does, I would test it out. I believe it is designed to store vacuum for use in the control of vacuum actuated items during low engine vacuum situations.
Le Mans Master
Joined: Jan 2001
Posts: 6,723
Likes: 1,377
Artey
Makes sense that it would be a vacuum leak. My Ford Bronco did that when I got a leak in the plastic line going to the a/c controls. I noticed that it would this at higher RPMs and it did make sense since vacuum deteriorates (goes away) as the throttle opens. (I ended up replacing all that crappy plastic tubing with rubber vacuum hose and never had any issues with vacuum again....).
That would also be why you'd have max vacuum at idle and lower engine speeds.
I would search for a leak on your hose leading the a/c controls.
Makes sense that it would be a vacuum leak. My Ford Bronco did that when I got a leak in the plastic line going to the a/c controls. I noticed that it would this at higher RPMs and it did make sense since vacuum deteriorates (goes away) as the throttle opens. (I ended up replacing all that crappy plastic tubing with rubber vacuum hose and never had any issues with vacuum again....).
That would also be why you'd have max vacuum at idle and lower engine speeds.
I would search for a leak on your hose leading the a/c controls.
Melting Slicks
Joined: Feb 2018
Posts: 2,323
Likes: 720
From: Marietta GA
A simple test is to turn off your engine wait 10 minutes and pull the headlight ****. I will bet you a beer, that your headlights doors won’t open! I installed all new rubber vacuum hoses. Except to the HVAC and my lights open / close great, but the engine has to running. I can live with it the way it is.
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