Lubrication can be applied sparingly of course, only as much as required, i.e. not slathered on in great gobs.
PAG oil must
NEVER be used to lubricate O rings, as this will cause corrosion to form at the joints, both causing leaks and making subsequent dismantling troublesome.
Instead a standard mineral oil can be used, or indeed as you have already heard rubber grease, neither of which will cause a problem.
The main type of joint employing an O ring in the A/C system is that of a parallel flange, so completely unlike both the taper joints used in hydraulic systems, and the flare nut unions employed in fixed brake lines.
PAG oil is very hygroscopic, so you will want to have the system either recovered before you start, or left open for the least amount of time if it's already empty, and the person who recharges the system must vacuum the system, both to test for leaks, and to remove any contaminated PAG oil, which will damage the system due to acid formation.
The oil grade is PAG46 and the dry fill quantity is 120cc with 450 grammes of R134a
Brian
