To improve engine cooling without the air conditioning operational, wire-up the air conditioning fan (in front of the condenser and radiator) with an independent circuit and your engine will run about 15 degrees cooler when “inching” in traffic on hot days.

The temperature gauge in my 1974 BMW 3.0SA would reach midway between the last normal mark and the red overheating mark when standing for lengthy periods in our big-city traffic on days in the 90’s. (The last normal mark is about 200°F.)

With the air conditioning operational it ran a bit cooler (10°F.), indicating about one fourth the distance between the two marks thanks to the air conditioning fan being operational.

With the auxiliary fan operating and the air conditioning off, the temperature indicator reaches the last normal mark, which is about 15-20°F. cooler, when in inching traffic for lengthy periods.

To effect the wiring, I picked up a hot lead controlled by the on/off key, installed a BMW switch on the dash and then wired into the positive air conditioning fan lead (red) between the fan and the flying fuse (16 amp).

In certain cases, care must be exercised not to operate both the air conditioning and the auxiliary fan switch at the same time. Two positive wires going to the fan at the same time might blow the flying fuse if the hookup has the opportunity for feedback. A relay protects the flying fuse when the air conditioning is not operational.

Author: Gary L. Vesey