If you're replacing a compressor I would advise using a reman unit from Mercedes to safeguard against problems later. That would also be the perfect time to switch to HFC-134A. If the conversion is done correctly you should have no problems with reliability. And yes, you may feel a temperature difference when the system is functioning in high temp and high humidity conditions the vent temp may be as much as 10 degrees higher.

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ASE Master Technician, Lead Technician for Deutsch American Inc. Over 6 years of Import Service-specializing in German Automobiles.