GM R12 to 134a Conversion

[Gordo24]

Hi all. I'm working on my 1976 Pontiac Bonneville, 6.6L/2B Brougham. Original VIR system being converted to 134a. When I took possession of it a while back when my grandfather passed, it had no A/C compressor and I had no idea how long the system had been open. Fast forward to today. I've taken the original evap core out and sent it to ClassicAutoAir in Tampa, they pressure tested it with Nitrogen to 350psi and it passed. Re-installed the evap core. It has a brand new condenser. I'm using a reman A6 compressor from Four Seasons (weak link possibly?) that has 10.5 ounces of Ester oil and +/- 1/4 oz of UV dye . I made new hoses and bought the VIR eliminator kit from ClassicAutoAir.com http://www.classicautoair.com/1976_Pont ... inator-kit
I also bought a vacuum pump, a refrigerant scale, a good set of manifold gauges and a 30lb tank of 134a.
The original R12 system called for 3.75#. I learned that an R134a system requires only 80% of what an R12 system requires. That figuring out to 3.0# of refrigerant. I added the dye and oil and vacuumed it down for an hour. I then leak checked it for another hour. All good. I go to put the 134a in and it takes forever (15 min) to get the 3.0# in. The car is idling at 15-1750 rpm with the A/C on high/max settings. I also cannot get the A'C clutch to cycle off, I've tried adjusting the low pressure switch on the accumulator but no joy. It's just not blowing cold (Maybe 60 F). My pressures at idle and operating temp are 47 low side/274 hi side, ambient temp was around 90.

I'm close but I'm missing something, I'm sure. I'm also thinking that I'm gonna need a real good dual electric fan set up on the condenser. Could it be overcharged? Because when I started adding refrigerant, the clutch was cycling on and off but eventually it just stayed engaged.

[Dougflas]

So now you have converted the system to a cycling clutch system. A6 compressors have a rather small clutch contact area. They were not meant to cycle. GM tried that and found that they had to increase the clutch area; hence, the birth of the R4 compressor. we all know how they held up. You adjusted the cycling switch which I would not have done because now you do not know where it should be. To test the system, run engine at 1500 rpm, max fan/cooling, recirc mode. I believe you are going to find the high side too high indicating air flow across the condenser a problem. make sure all of the shields are in place. You may have to place a fan in front of the grill. If the high side is still too high, mist the condenser with a hose. If the pressure drops like a rock, that is the area of your problem.

Hopefully, you have put the evaporator back into the vehicle with all the seals intact, and the blend door seals are in good shape. Also, check the calibration of your thermometer. It should not have taken you that long to charge the system. If you have an accumulator, you can charge with liquid and not slug the compressor.

[Gordo24]

This is my setup. My first attempt at a conversion. Where can I charge it liquid?
I was meticulous with the seals and I replaced all the brittle foam as well. I made patterns from the old ones and it seems to have worked well using semi closed cell foam.
I'm only getting 60F at the middle vent on max recirc

[Dougflas]

Black cap on accumulator if you have a regular hose end

[Gordo24]

I'm thinking it's the condenser. And I'm also leaning toward an overcharge. I put 3 lbs. in from a 30lb. tank on a digital scale, the first pound or so I put in as liquid, then I turned the tank back up and switched to the low side to add the remainder. The R12 capacity is 3.75#. Is the 80% of R12 ratio set in stone or is it a more of a 'watch your pressures on your gauges' kinda thing? I'm thinking I put too much in.
The pressures do drop significantly when I spray the condenser with water. Like, WAY down on the high side. It drops almost 100psi in a few seconds, so that leads me to believe that I either have an obstruction somewhere and/or the stock condenser isn't cooling efficiently enough. I'm looking at parallel flow units right now. Can anyone recommend a new A6 to me? Still getting 62 deg. vent temps and I was going 40 mph as well.

[Cusser]

Is the 80% of R12 ratio set in stone ?

It's a starting point; the experts say some will require less than 80%, some will require more than 80%.

[bohica2xo]

So, where did you put the oil when you charged it?

[Gordo24]

In the suction port of the compressor. I did hand crank the compressor also.

[bohica2xo]

Did you pull the drain plug on the compressor sump & make sure it was not shipped with an oil charge installed before you mounted it?

Ideally,oil should be added to a fresh A6 on the bench through the sump plug

The A6 has plenty of room inside. Problem is, an overcharge of oil can really hurt system performance.

[Gordo24]

Did you pull the drain plug on the compressor sump & make sure it was not shipped with an oil charge installed before you mounted it?

Ideally,oil should be added to a fresh A6 on the bench through the sump plug

The A6 has plenty of room inside. Problem is, an overcharge of oil can really hurt system performance.

I took the protective plate covering the ports and let it drain for a day.
Update: I'm getting 38 degree temps at accumulator so I know the system is working properly. It seems that when i re-installed the evap box on the firewall I didn't get the bottom left to seal properly. Therefore it was sucking a huge amount of outside air into the box and out the vents. I broke the case open and rectified that situation. I now get 43 degrees out the center vent. BRRRRRRRR
Thanks for the help fellas.