I've had this 1988 420 sel for about a month a think it's a great car. As the weather heats up, the a/C just doesn't seem to be cool enough. I notice some oil leakage around the the flexavble line that leads to the evaporator when I first bought the car that seems to have stopped. How often should the A?C on this car need to be recharged with coollant or is it likely just leaking?

The A-C system is charged with refrigerant not coolant but you didn't know and now you do. The systems in theory are a sealed unit and therefore should not ever need to be charged unless there is a leak. If the leak is large enough to warrant parts replacment, you might consider to convert to R-134A instead of the R-12.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

I have a 1986 420SEL, live in Texas, have had it for 3 years. 100K miles. AC has never had Freon 12 added and it cools very good. Only complaint is the fan in auto mode blows very forcefully and loudly.

So have your checked for leaks. I would doubt a 134a conversion would be very satisfactory. No one I know in Texas who has done a conversion has been satisfied.

Just a note, Most of my 134-A conversions work as well if not better than the r-12 systems. The thing to getting these cold is the proper condenser core and aux fan combo.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

I would expect that a 134a conversion would have to increase the size of the evaporator too to really cool as well as Freon 12. 134a just doesn't have the same specific heat rating as 12. Do you live where it gets HOT like Texas?

Yes, Atlanta GA! It gets HOTTT here too. The size and efficiancy of the condensor is the key to getting the air cold not the size of the evaporator.

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM