944 A/C Condenser Leak

[dr bob]

The oil discussions are pretty settled. For conversions that don't include flushing, using the ester oil rather than Denso's recommended PAG, is purely a question of how much gelled sludge you can tolerate. In an expansion valve, it dramatically limits flow and system performance. On heat exchanger surfaces, it's an insulator and slows heat transfer. Not worth the risk in my casual experience. Using the correct oil is only slightly less convenient than using PAG, and that's only if you are installing a new compressor already filled with PAG. If you are buying a fresh bottle for your project (and you should...) anyway, grab the light-green synthetic polyolester and worry none about it.

For a longer period of years watching folks do their own 'conversions', more than a few owners complained about how the R-134a just didn't cool the cabin as well. It was pretty easy to see where the small details, like not replacing the oil in the system with the correct oil for the conversion, not changing changing ALL the o-rings, not using barrier hose, and not evacuating the system completely before charging, make the difference between ice-cubes air temps and the ~~50ºs they were seeing. Of course it's gotta be the refrigerant! Meanwhile, the system thrives on care and cleanliness, performing every step of the work, and in our cases we must get the charge levels exactly correct without relying on the sight glass.

Miss any of the steps, and at minimum, performance suffers. A few, like draining and replacing using the correct oil, are critical to both performance and system longevity. PAG and the old mineral oil used with R12 form a gel that restricts flow, plus the new oil that bound in the gel no longer lubricates the compressor, including wetting the mechanical seal on the drive end. The simple choice of ester over PAG as replacement eliminates that risk completely.

Installing a fresh Denso compressor in a flushed-clean system? Sure, the PAG they ship in the compressor is fine. Just drain it out completely, pour back in the exact amount the whole system requires, and you are good to go! For the rest of us mere DIY mortals converting our own cars, ester is the right choice.

In my limited experience with such things...