I'm converting my '89 740 from R-12 to R-134.

The A/C was never charged enough during my ownership to actually "see" it work, and the system is too much apart (disassembled) retrofitting, replacing the compressor, and all O-Rings and the Accumulator to dare activate the electrical circuits.

I want my pusher cooling fan in front of my A/C condensor to run when the compressor clutch is engaged to help make my A/C system more efficient, because the car will be moving to Phoenix, where it will need all the help it can get.

I was going to power it with a small 30a relay controlled by the compressor clutch and wired to the fan from the battery through an inline fuse. The fan DOES run when the coolant temp reaches 210 deg F, I believe so the fan would now also come on ANY time the compressor is working (via the relay).

But I started thinking MAYBE it's already wired that way from the factory?? My book doesn't say one way or the other.

I tried to follow the teeny, tiny wiring diagram in my Haynes manual until my head hurt, but I couldn't find the circuit, so maybe some of our members could tell me if their pusher fans automatically come on when the A/C is on, or at least when the compressor clutch is actually engaged and making pressure.

Also, I wonder if I should install diodes in the fan power feed wires if I DO install the relay, so the power from the compressor-on relay can't do any harm "back-feeding" the rest of the fan circuitry?

Thanks,
Bob