Hi

Posting this mostly to help anyone else who is looking at a thirdgens AC system in the modern era. you'll find a lot of posts here from through the years of people fighting about wether or not it's possible to have a successful r134a system in these cars. I personally think a lot of that is because of the varying ways that people attempt to solve the problems with thirdgen AC, and also the availability of certain new that did not exist when they were posting.

ANYWAY. So on to what worked for me:

The number one most important thing I learned after multiple compressors and charge attempts. The GM R4 compressor, wether reman from any company, or new from GM, is never to be trusted. at this point any R4 compressor you get from anywhere is liable to have been sitting on the parts shelf for years at this point. I personally had 2 new GM genuine R4 compressors blow the case seal within a week of changing.

Enter GPD.....

GPD, makes an R4 sized compressor but what's special about it is that is actually a modern scroll type compressor(like what r134a factory cars have). this GPD compressor is not the one that comes up when you look for parta for these cars on Rock Auto. (Part #7511370). That part is the STANDARD R4 TYPE.

the scroll type is 6511348. This compressor has the correct grooves for our drive belts, but its clutch pulley is slightly larger than the factory pulley.

This requires you to use a slightly longer belt. in the case of my 305 TBI this belt is AC Delco part 6K935.

I then also replaced the condensor with GPD 3231C. This is a parallel flow condenser, which is designed to work efficiently with an r134a system. alot of previous threads where people converted the factory system to 134, they retained the factory tube and fin condenser. That's a huge part of their problems.

I also chose to replace the compressor hoses with GPD 4811708.

From previous forum posts and a YouTube video of a guy with a similar scroll type compressor, I decided to use Motorcraft YG346 RED fixed orifice tube.

I used the GPD drier bottle, part 1411347.

Lastly I used the GPD 4711411 evaporator coil. this is probably the most important part of the puzzle. the factory evaporator has a ton of built on closed cell foam. you can't remove it without it breaking and it also is already shot by the time you get in there. I did not do this originally and I chased 60F vent temps on an otherwise perfectly operating system. The following is the second most important thing I think that I did for the system. I ordered new 3/4" squares of closed cell foam from Amazon and put all around the evaporator coil. The idea is you need to be DANG sure that the air has NO path except through your new evaporator coil. On ALL of these cars, unless you address this, it will be a weak point. look at the below photos:






Seal any box cracks with rtv. And get foam in any path air can bypass the evaporator.

Lastly, my blower label says 2.25 lb of r12. If you convert that to r134, that's about 28-30oz of 134. I don't know why, but there's tons of conflicting information. I found the correct capacity listed as 3LB of r12. This converts to more like 38-40oz of 134a. This amount was correct in my case.

Current vent temps at 90f full sun load:





Don't let anyone tell you you can't have an r134a system that performs.

 

Excellent write up, thanks for sharing! I've been thinking about getting my AC fixed up for the last 7 years or so, might finally be time if a recharge doesn't work (my system was retrofitted for R134a before I got the car, but stupid teenage me broke off one of the pressure fitting caps and let most of the refrigerant out back in 2019 ). Anyways, for the compressor, did you have to do any rewiring at the plug/ did the stock brackets work?