We have a 1988 Mercedes 560SL. The car wouldn’t start, but this was fixed by replacing the fuel pump relay. However, the a/c compressor then failed to operate. We checked that refrigerant is o.k., the blower works o.k. and we have put in a new a/c relay, but the compressor still fails to switch on. We still wonder if this is related to the fuel pump relay, since the failed nine-pin unit was superseded by a new replacement unit which is now ten-pin. Is there anything else we should have done when replacing the fuel pump relay, or any other part we should check?

The Receiver/Drier is located in front of the radiator and condensor,after locating the rec./drier find the low pressure switch attached to the rec./drier (it's the one without the pigtail,jumper these two wires and start the engine and turn on the a/c.If the compressor engages the system is low on refridgerant.
Good luck and post your fix. Mike