Mercury Repair Questions? Ask a Mechanic for Answers ASAP
The P0645 is a fairly straight forward code pointing to a problem with the A/C Compressor Clutch Relay. The Relay is located in the under-hood fuse/relay box. You can temporarily swap this relay with another from the box with the same numbers (I believe fog lamps is the same relay). If the swap solves the problem, replace the relay. You can order one at most local parts stores by using the numbers on the side of the relay. If the swap does not solve the problem, then there is a problem with the wiring between the relay adn the on-board computer, or the on-board computer itself (which isn't very common). Remove the fuse/relay box and make sure all the connections are tight. If so, the wiring harness will need to be carefully inspected for any broken or damaged wires. For an image view of the relay location, click here: https://www.dropbox.com/s/3bgefp62lx6u3eu/ac-relay.jpg?dl=0
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