You have a leak. I have attached a chart showing the pressure variances between R12 and R134a. It is not necessary to change the pressure cycling switch as once popularly believed but as you can see from the chart there is a few pounds of difference and it should help the retrofit system perform better. When I used to sell parts I remember there being two cycling switches available to cover the emerging retrofits when R12 was being phased out. Most aftermarket manufacturer's have phased out the second part number and have replaced it with an adjustable model. You will see the screw between the two terminals.
In regards to your leak check some oils are not compatible and you have to ascertain what is in the dye you intend to use. Many cans of R134a with leak dye also have oil in them. PAG Oil is not compatible with mineral oil. Ester oil is the right type of oil for retrofits and Ester 100 should be fine for our GMs. I don't like mixing large amounts of different oils together. If it was me I see a couple of options
1.Find a creative way hooking up regulated air pressure (30 psi) and looking for leaks, then drain as much of the oil out of the system and start over with oil and freon once the leak is repaired and the system integrity is confirmed.
2. Drain the mineral oil out, add the appropriate amount of ester oil and charge the system with R134 with dye, and then find/repair the leak. If you go back with R12 I would do a clean and flush before final charge either way.
Lastly, I think you have a big leak judging by how fast it dropped. The best way to find large leaks on low cash is option 1. If you are hunting a real slow leak sometimes you need to do step 2 and even run the system to really find it. Cost of Freon doesn't matter a bunch if you have a recovery machine, but most of us don't.
Just out of curiosity have you priced R12 in your area or did you have a stash laying around? Once people see what that costs they usually go to R134a. My car is ice cold with R134a FWIW.
In regards to your leak check some oils are not compatible and you have to ascertain what is in the dye you intend to use. Many cans of R134a with leak dye also have oil in them. PAG Oil is not compatible with mineral oil. Ester oil is the right type of oil for retrofits and Ester 100 should be fine for our GMs. I don't like mixing large amounts of different oils together. If it was me I see a couple of options
1.Find a creative way hooking up regulated air pressure (30 psi) and looking for leaks, then drain as much of the oil out of the system and start over with oil and freon once the leak is repaired and the system integrity is confirmed.
2. Drain the mineral oil out, add the appropriate amount of ester oil and charge the system with R134 with dye, and then find/repair the leak. If you go back with R12 I would do a clean and flush before final charge either way.
Lastly, I think you have a big leak judging by how fast it dropped. The best way to find large leaks on low cash is option 1. If you are hunting a real slow leak sometimes you need to do step 2 and even run the system to really find it. Cost of Freon doesn't matter a bunch if you have a recovery machine, but most of us don't.
Just out of curiosity have you priced R12 in your area or did you have a stash laying around? Once people see what that costs they usually go to R134a. My car is ice cold with R134a FWIW.
