The Tiniest Mistake

Is faulty HVAC diagnosis costing you money in the cold of winter?

Want to make a quick $10,000? DeGuiseppi makes a standing bet with all his students that if they can find a light-duty car or truck that has ever left an assembly plant with any kind of oil in its R134a A/C system other than polyalkylene glycol, or PAG, he will fork over ten grand.

"Since the beginning of R134a, there's been no other kind of oil recommended for use in production R134a systems by an OE vehicle manufacturer other than PAG," he says. "But of course there are other types of lubricants on the market that some people insist on using. This is the biggest mistake out there."


Retrofitting an R12 system to R134a? In 99 percent of retrofits, DeGuiseppi says, PAG is the recommended oil.

"But, there are a few vehicles--a scant few--that do recommend another type of oil called ester, or polyol ester, and in those cases those are the ones you should use," he says.

"Back in the day, PAG was a lot more expensive than ester," he continues, "and for some reason it got into the psyche of many a technician that ester was the 'universal retrofit oil,' and there never has been such a thing."

DeGuiseppi adds that, although there are different types and viscosities of PAG oil that are recommended for different compressors, PAG is all your technicians should ever use.

MACS offers several classes that can keep your technicians up to snuff on what DeGuiseppi describes as "the pretty drastic changes that have taken place in A/C systems just in the last five years: smaller charges, smaller amounts of oil, different strategies for compressor clutch engagement.

"If it's been more than a couple of years since your technicians have taken a training class," he says, "get them one."

Even if it's in the dead of winter.

For information on MACS training classes, visit

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