A/C Question
Thread Starter
Pro
Joined: Jul 2004
Posts: 605
Likes: 0
From: Alta Loma CA
A/C Question
I have a '73 Corvette that has an accumulator system adopted from an '78. It is converted to 134. I had a local shop make hoses and charge it. It has never been able to cool as well as other ones I have heard of with the same set up. I checked the pressures and found 25 low 100 high. Temps were as low as 53. So I added freon and got up to 40/165. Temp dropped to 50. It took about 2/3 of a can. Then after running for about 20 minutes temps went up to 60.
What do you guys think? Is an evac and recharge what is needed?
What do you guys think? Is an evac and recharge what is needed?
Burning Brakes
Joined: Jun 2008
Posts: 1,086
Likes: 1
From: Michigan
The temp of the air coming out of the vents is also controlled by a flapper door in the distribution box. There are two flappers, one is temp and the other is direction (floor, vents, defrost). Perhaps the temp flapper is not moving freely to the closed position and you are getting warm air mixed with the A/C air.
The temp door is a vacuum/mechanical operation. You should be able to see the lever moving under the dash at the distribution box as you roll the temp wheel at the center console. It may not be closing all the way or perhaps the seal is not sealing when it is in the fully closed position.
The temp door is a vacuum/mechanical operation. You should be able to see the lever moving under the dash at the distribution box as you roll the temp wheel at the center console. It may not be closing all the way or perhaps the seal is not sealing when it is in the fully closed position.
Drifting
Joined: May 2002
Posts: 1,546
Likes: 282
From: Back in Nebraska
I have a '73 Corvette that has an accumulator system adopted from an '78. It is converted to 134. I had a local shop make hoses and charge it. It has never been able to cool as well as other ones I have heard of with the same set up. I checked the pressures and found 25 low 100 high. Temps were as low as 53. So I added freon and got up to 40/165. Temp dropped to 50. It took about 2/3 of a can. Then after running for about 20 minutes temps went up to 60.
What do you guys think? Is an evac and recharge what is needed?
What do you guys think? Is an evac and recharge what is needed?
Limping across the line
Joined: Oct 2002
Posts: 5,299
Likes: 109
From: Peoria Az
Make sure your radiator cooling fan is up to the task.
If your head pressure(Hi Side) gets to high, cooling will suffer.
A good radiator fan is crucial to keeping head pressure low.
As a general note R12 systems converted to 134 should only be charged to about 3/4 of R12 capacity. If too much 134 is added system performance degrades. Unlike a r12 system where a overcharged system has no consequence on cooling just your hi side starts getting too hi.
When doing a charge after swapover I stop adding 134 when accumulator is cold to the touch. Newer 134 systems run about 200 on the high side with low side being 30-35 psi
If your head pressure(Hi Side) gets to high, cooling will suffer.
A good radiator fan is crucial to keeping head pressure low.
As a general note R12 systems converted to 134 should only be charged to about 3/4 of R12 capacity. If too much 134 is added system performance degrades. Unlike a r12 system where a overcharged system has no consequence on cooling just your hi side starts getting too hi.
When doing a charge after swapover I stop adding 134 when accumulator is cold to the touch. Newer 134 systems run about 200 on the high side with low side being 30-35 psi
Le Mans Master
Joined: Aug 2003
Posts: 7,720
Likes: 12
From: Chattanooga TN
I have '82 Evaporator and Condensor, '91 Nippendenso (C4)compressor, custom lines. I am running R12 and it is very nice and cold. To use the '78-82 parts on a '68-72 anyway, you have to grind some on the fan housing or it hits the inside of the fender.
Thread Starter
Pro
Joined: Jul 2004
Posts: 605
Likes: 0
From: Alta Loma CA
Just to add to this. I have dual electric fans that keep the temp more that low enough. So that is not a factor. I also know all flapper doors are closed as they should be. Car has both heater hose with shut offs and the whole interior floor and firewall are insulated.
But what I don't uinderstand about it is why the pressures don't go up higher. That's why I think it needs to be evacuated and get a new charge. But I don't know if that's a correct assumption.
I appreciate everyones advice so far.
But what I don't uinderstand about it is why the pressures don't go up higher. That's why I think it needs to be evacuated and get a new charge. But I don't know if that's a correct assumption.
I appreciate everyones advice so far.
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
With your pressures and not knowing the ambient temp this is a wild guess, but your compressor might not be in the best of shape. To test, block the airflow to the condenser and read the pressures. Changing the oriface tube can help too.
If you doubt the shop's charge, the only way to is to evacuate and recharge. Then you still have no idea of the amount of oil in the system. The ideal way is to remove all the components, flush, reinstall, add oil, evacuate and charge. Most people don't want to go thru that.
BTW, although sometimes you can get decent temps with the stock condenser, 134a needs a parralel flow condenser to work as well as r12.
If you doubt the shop's charge, the only way to is to evacuate and recharge. Then you still have no idea of the amount of oil in the system. The ideal way is to remove all the components, flush, reinstall, add oil, evacuate and charge. Most people don't want to go thru that.
BTW, although sometimes you can get decent temps with the stock condenser, 134a needs a parralel flow condenser to work as well as r12.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
5 Best & 5 Worst Corvette Daily Drivers
Joe Kucinski
The Headlights of Every Corvette Generation Explained
Joe Kucinski
5 Best & 5 Most Overrated Corvette Track Packages of All Time!
Joe Kucinski
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
