PeachParts Mercedes-Benz Forum - View Single Post

Diseasel300 · #33 05-13-2020, 11:35 PM

70% you're way undercharged. Having recharged many Gen II's, the ideal weight for an empty system in our climate is 42 ounces. Factory charge is ~46 ounces. Roughly 90% of the R12 charge by weight. Lots of armchair experts like to quote hard numbers when converting "because that's what the Internet said". Most of them are also the same ones that ***** about their converted A/C being weak. Charging a converted system is more of an art than a science, you're not dealing with the factory weight of refrigerant specified by the engineers who designed it.

If you're uncomfortable going straight to 42 ounces, add in 36 ounces, park a reliable temperature probe in the center vent, fan on Max, temp wheel on min cold, all 4 doors wide open. Continue very slowly adding gas in short bursts and watching the temperature gauge in the center vent. Keep adding gas and waiting (1-2 minutes) in between additions until the center vent temperature is 30˚F below the ambient temperature (if it's 85 outside, keep adding SLOWLY until you're at 55). If you want to get the charge perfect, continue adding very short gas bursts and giving the system time to equalize between additions until you see no further reduction of temperature at the center vent. You'll find you added 41-42 ounces of 134a.

Having been charging Fords, Hondas, Mercedes, BMW's, Mazdas, Mitsubishis, Chryslers, GM's, and too many others I've forgotten about over the years, I can promise if you charge the system carefully and deliberately, you'll have ice-cold air with 134a.

Your head pressure will be higher than you expect it to be on a modern car. Ignore that. You're dealing with a converted system, the head pressure will be higher at a proper charge. The Denso compressor will handle it no sweat. The head pressure will actually DROP once you're moving and have air blowing through the grille and the system catches up with the heat load in the cabin.