I have always used the "ester" oil with no problems.

 

I found another forum that recommends using PAG-42 (low viscosity) if you completely flush the old mineral oil from the system. I should only have to purge the evaporator core and the compressor, so I would like to use the PAG.

Apparently, Ford does not recommend the ester oil, even though it will not react with mineral oil.

Is this true?

 

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They will recommend "BVA Ester 100" oil just in case you ever want to go back to R12, and if you don't get all of the old mineral oil out, it won't be an issue.

If you use PAG oil, be sure to use a "DEC" or double-end capped, which means it is significantly less reactive with water.

Be sure to pour oil in the suction port of your compressor and rotate it by hand to push out the mineral oil. Let it drain for at least a day - you'd be surprised how much will drip out overnight.

Dan