I have a question - I am going to do the R134a conversion to my stock 1987 with 305, and have installed new o-rings & accumulator, and vacuumed the system to make sure there are no leaks. I need to know the following information: How much oil is needed, and also how much R134a? Is there a certain amount that must be put in, or is there a correct pressure that it must be filled until it gets the correct pressure? Also if I draw down the vacuum overnight, will it remove all of the old oil, or do I have to remove the compressor and drain the oil from inside?

Also, I read somewhere that if one uses a Ford orange expansion tube (oriface) instead of the white Chevy one it will work better. Any reason for or against this? I put in the orange one since it is only a couple of bucks, but not sure what difference it will make if any.
A relative newcomer to ac systems,
Dave

hello: just read your post, did you ever get your A/C system going??
Darryl...

Why are you switching to 134A? R-12 is available.

Well as a do-it yourselfer I was not able to get any R-12, only a licenced technician can buy it (in CT anyways) but all of the outo parts stores sell the R134a. I put on a new dryer, expansion valve, oil, (after vacuuming it out a few hours) and new o-rings after we found some leaks. It works ok, but not as cold as I would like, not sure if I should add more R134a or if too much would cause this problem?
Dave

Hello: R134a is not as forgiving as R12. This means a tad to much or a tad to little can affect performance quiet a bit. Being from CT you should be able to get it to work pretty good though at least to provide cooling up in that neck of the woods. You will use less R134a in your system than R12. Make sure your clutch on the fan is working, maybe just get a new one. Also might want to find a 7 bladed fan to stick on the front. I have found in my experiments an awful lot of air escapes around the radiator from the engine compartment . If you could fabricate something that would block air from escaping the engine compartment and being recirculated through the condenser. Oh! you have no expansion valve, but an orface tube. Is the return line from the accumumulator getting cold?? Do you know if your compressor has a high pressure cut out switch on it??. Also can adjust the low pressure cut off switch a little to cause it to pull down a little lower. Will need gauges attached to see if this is working. Have had these switches go bad and cause poor compressor operation. This is the switch screwed into the accumulator.
Good luck
Darryl...

you can still buy r-12 on e-bay

As stated before make sure there is enough airflow through the condenser. To start with,connect your tank to the car and with the engine off open the red high side valve and let the pressure equalize with ambient air temp. Close the valve. Next with your manifold set (gauges) hooked up the high side pressure should be approximately 3 times ambient air temp. minus 50 pounds. For example the air temp outside of your car is 80 degrees: 3 X 80 =240 - 50 =190 lbs on the high side. Your low side pressure should be around 25 -35 lbs at 1500 rpms. Note you may need to have a gallon of water handy to splash on the condenser if the air temp is very high so your pressures will come down. Just take your time and don't add but little squirts, through the low side, at a time if adding while running.

UncleGus

you can buy R-12 on ebay only with a license. if one sells it without checking and the buyer is undercover agent, the fine is huge.

With a R134A conversion I add freon until the high pressure is about 200psi (air temp about 80) which works out to about 10% less than R12. Seems to work well as I have done many conversions. If you completely flushed the system add the oil that the manufacturer specs.