Hello!

I know this question's been asked before, but I don't recall ever having seen a definitive answer.

I finally got my hands on a working electric fan for my car (the one that goes in front of the a/c condenser). IIRC, on some cars, the fan activates whenever the a/c's operational, while on other cars, the fan activates when a pressure switch in the high-pressure a/c line tells it to, while on other cars, the fan turns on when the engine coolant temperature's high enough to activate a sender. Some cars go on any combination thereof, so I hope people understand when I say I'm really confused.

I know that my fan works; I just hooked it up directly to the battery and it spins nicely. However, with the engine off but the key at "ON" and the ACC set for the air conditioning, the fan doesn't work. How can I find out when exactly my fan's supposed to turn on and when it's supposed to be off?

Thanks in advance! This is (of course) on the '85 300D.

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2001 VW Jetta TDI, 5 speed, daily driver
1991 Ford F-350, work in progress
1984 Ford F-250 4x4, 6.9l turbo diesel, 5 speed manual
Previous oilburners: 1980 IH Scout, 1984 E-350, 1985 M-B 300D, 1979 M-B 300SD, 1983 M-B 300D
Spark-free since 1999