Pipe dope and sealant

[JCTyler]

I'd like to know what kind of pipe sealant is used on auto a/c fittings that are NPT and NPS? Would pipe dope be used?

[JohnHere]

I wouldn't use any kind of plumbing pipe dope for NPT or NPS fittings because of the risk of contaminating the system with incompatible substances.

I wouldn't use plastic tape on the threads, either, because any remnants of the tape that inadvertently find their way into the system could clog critical components.

Nylog Blue is the only sealant I know of that will do the job and that is compatible with MVAC systems.