I think it is a good idea to wire the fan to run with the AC compressor regardless of the coolant temperature. I was at my mechanic's shop on Sunday repairing my AC and we had all the gauges hooked up so I could see the pressures. We got nearly double the high pressure without the fan; the low pressure was up considerably as well and the temperature coming out of the vent was similarly high. With the fan on, the high pressure dropped fast and stayed at a good range and the low side went down and the temperature coming out of the vent dropped considerably.

You need a one way diode and a relay if you attempt to do this; you do not want to wire so that the AC comes on whenever the fan comes on. The diode is needed to block the fan switch power from feeding the compressor.

Philip Bradley