sdellinger,
was the system converted previously to r134a or are you now converting to r134a?
if you are converting now, system has be be flushed by approved a/c methods for long life of the comp. there will be remnants of old r12 and old lube in system.
if previously converted, there is still some lube in the hoses, mufflers, evap. and condenser. 4 oz add. will be enough.
http://www.id-usa.com/how_to_faqs_retrofitting.asp#9
8. Why does Interdynamics use Ester Oil instead of PAG Oil?
While both lubricants are used with R-134a, Ester is believed to be better for Retrofit systems because it is compatible with the residual mineral oil left after evacuating a R-12 system.
In addition, Ester oil is a preferred top-off oil because it is compatible with ALL PAG Oils and is much less hygroscopic, which means that it does absorb as much water from the atmosphere as PAG Oils do. This moisture can create problems in a vehicle's A/C system.
Ester is also a truly Universal lubricant which has a Single Viscosity. PAG Oils come in a variety of viscosities which must be matched to the vehicle. GM vehicles use a high viscosity (150) PAG Oil, and non-GM vehicles use a low viscosity (46) PAG Oil. You cannot use a 100 viscosity PAG Oil as a "1 size fits all" universal lubricant. Ester Oil, however, is truly universal and will lubricate properly regardless of viscosity.
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9. Do I need to remove the oil that's in the system? Is the old oil compatible with the new oil?
No. The residual mineral oil left behind after you evacuate a R-12 system will not mix with the new R-134a refrigerant. That is why we add Ester Oil, because it will mix with R-134a, lubricate the system components and is compatible with the residual Mineral oil.
The mineral oil just collects in a low place in the system (such as the accumulator), where it stays, until it is removed at some later date during future maintenance or repair. The mineral oil does no good, but it does no harm either. It's just there.
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PAG46 is also perfectly ok to use in converted Ford systems unless the compressor directions call for other spec'd lube
see
http://www.technicalchemical.com/tec...cantguide4.pdf
the most important part is complete vacuum evacuation, removing all the air and water moisture possible. best done by a shop with commercial equipment. no use buying another comp. in a year when this one dies from water corrosion