Vintage Air & M-21 Question


Jun 3, 2021
I have finally come to the conclusion that I will not survive another summer without A/C while cruising. In my teens, neither of the two Camaro’s I owned had A/C and I cannot remember ever complaining. It has taken me a while to make the decision to add the A/C kit to what I consider a ”mostly“ unmolested engine bay on the ole girl but I will eventually get over the new look , as she will still have her “born with” drivetrain.
Now for my question, what can I expect as far as issues, if any, having a close ratio transmission on an A/C car? Thanks for any input and apologizes if I missed this topic on the topic search.


Veteran Member
Mar 24, 2009
San Gabriel Valley, California
I have a vintage air kit with an m20 4 speed and while it has only been one season so far I have no problems. I have ripped through the gears with the AC on and nothing has broke. I shift at 6k though. The compressor the kit uses is supposed to be capable of high rpms. I've been happy with the kit. And yes I'm older now too and less tolerant of the heat. When I found myself skipping drives because it was too hot I knew it was time to install AC.


Jun 3, 2021
Me too on a few cancellations this past summer Mike. Just wondering what to expect after installation of the kit with the m21, since they weren’t an option when you ordered a car new.
By the way, no 6k shifting here☹️..
Thanks for your thoughts on this..


Veteran Member
Sep 24, 2014
Pittsburgh, Pa.
I have the VA and an M21. No problems. I could be wrong, but I think it shuts the clutch off at a certain RPM to avoid damage to the compressor. One of the best mods I ever made. Stuck in gridlock for an hour and 40 minutes on a high temp and humid day and swore right then and there I was putting air in. I'm old too, and figured most of the time I would be driving it, it would be on nice hot days.

Gary S

Lifetime Gold Member
Apr 14, 1999
Bismarck, North Dakota
The tranny doesn't make a difference with A/C. The M21 will work just the same as an M20 would, and it will work the same with A/C as it did without it.

Dave Nelson

Veteran Member
Dec 19, 2003
Vineland N.J USA
I have factory AC in my 70 SS L-34 with a M20 4spd still uses R-12, will freeze you out on the highway but the BB will tend to run hot in traffic with the AC on.

john Gialanella

Veteran Member
Oct 15, 2008
Bloomfield N.J.
Since your 1970 SS 396 has AC, you would have received the VO1 heavy duty cooling standard with 4 row (core) radiator. I am surprised you run hot. My 1970 SS 396 L-34 does not have AC. A few years ago, the 3-row core was leaking, so I had it rebuilt with 4 row core with original tanks and it never comes close to the center of the temperature gauge, even in hot summer days.


Veteran Member
Lifetime Gold Member
Sep 15, 1999
Ontario, Canada
When my original 2 core in 1981 went South, I had 4 cores built from it. I never get above 180* with a 180* stat. I would never add a/c in my car. My a/c is the windows rolled down and if it’s too hot, I don’t drive it. I have custom cloth seats so I never get a leg rash like I did in my 77,78 and 80 Z28’s with vinyl seats.