W126 A/C questions/problems - PeachParts Mercedes-Benz Forum

Diseasel300 · #2 01-09-2020, 11:22 AM

The high side valve is the one shown in your first picture. It is a standard 1/4" Schrader port for R12/R22. If you have a set of R134a gauges or if you're doing a proper conversion, you'll want to buy a quality adapter for it.

Since the system has been open, you want to flush the whole thing well. Drain the compressor, flush all the lines, remove the expansion valve (MAJOR pain on the W126) and flush the evaporator well.

While you have it apart, replace ALL of the O-rings on the various joints and smear them with Nylog before you reassemble. It'll save you from leaks for years to come. You're already in there, so why not.

Install a new filter/dryer. If going that far, replace the pressure switches on it, one controls the auxiliary fan, the other is a low/high pressure switch. Don't mess with the filter/dryer until you're ready to install it and switch on the vacuum pump.

The compressor is a Denso. It takes roughly 7 oz of oil. Consider using PAO oil instead of PAG. It has better lubricating qualities and is not hydroscopic (so it won't turn acidic from residual moisture in the system). It is compatible with R12, R134a, R152a, and Hydrocarbon refrigerants as well. The cap on the compressor is an auxiliary low side port. Leave the cap on. Replace the cap and Shrader valve if you feel like it.