Can I use ester oil in a ac system that calls for pag oil

Did you replace the orifice tube?

Here is the rule, you pour all the oil out of the old compressor and measure it, then you add that much back plus about 2 ounces. The oil should be virtually clear if it is dark or black flush the AC system with denatured alcohol and compressed air.

there will be no need to put oil in an ac compressor
new compressors already have oil in them and old units have the oil through out the ac system that comes back in with the gas.

the oil used in ac compressors is specific for the gas in use
new compressors have the correct oil already in the unit and a leaking system will not require any oil to be added
using the wrong oil will probably result in a system replacement

For the R134 A/C system on this van the amount of PAG oil is 7.4 oz. Adding too much oil will reduce the cooling ability of the system.

it will not eliminate the noise. you'll need to replace the bearings.besides from the knocking noise is the air coming out from the vents cold? when you recharge the freon is it totally empty? if thats the case you probably have a leak in the system . check all the lines and connections for leaks using liquid soap add a little bit of water to make it bubbly.start the ac and use a sponge.normally when there is a leak the oil will leak together with the gas so ypu'll need to add some refrigerant oil as well pag oil is best..but i'll need more details so i can help you out

System 7 to 9 oz

Condenser 1 oz
Dryer or Accumulator 1 0z
Evaporator 3 oz
Compressor 3 to 4 oz

On most vehicles

You have a big problem---no R12 has been avail for the
last 15 years

SO-- you need to flush every component of mineral oil
& replace with ester or pag,then switch to R134A refrigerant

That may require a compressor built for those pressures &
"o" rings such as the green ones

Need to research what your doing

A/C SYSTEM OIL TYPE 1983 Cadillac Seville 4.1L TBI 8cyl The A/C System Oil Type

SEE NOTE Ask about A/C repair & diagnostics DVDAll vehicles originally equipped with R-12 Freonwill require a complete system flush,draining comp A/C SYSTEM OIL CAPACITY 1983 Cadillac Seville 4.1L TBI 8cyl The A/C System Oil Capacity 6.00 Ounces

ressor oil & ultimatelyretro-fitting the vehicle to R-134A refrigerantand the compatible polyalkylene glycol (PAG) oil.

it is NOT recommended, BUT, it will usually work.

Do you have the old compessor? Drain out what is in there and use that amount as a guide + 1 oz. There is no ratio per se. As long as you are close without being crazy low (none) or crazy high (over flowing), you're good.