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.

__________________
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

I’m thinking this isn’t going to answer your question, but I spent some time wondering the same thing. I have an ‘80 300D that I bought new in Dallas, TX. For many years it ran winters and summers at the proper engine temperature range. Then one summer it started to run hot. The next year hotter than that. Well, that was about 8 years ago. I put a new pressure switch (that runs the fan) on the filter/drier, but that didn’t fix it. Some times with the A/C on I could hear it running. Sometimes not. Sometimes in traffic it would heat up to the point where I was rushing to get off and either shut it down, or get enough speed (air flow) to cool it down. I changed the engine driven fan assembly as well. Still no fix. I then pulled the two wires going to the pressure switch and found that a 15amp blade type fuse would connect the two of them together quite nicely. So now, every year when the outside temp hit’s the 80s, I put the fuse in. I take it out around mid November and plug the wires back into the switch. In other words: During the hot summer months, my fan comes on when the ignition switch is turned on. That was 8 years ago, and I’ve had no overheating problems in any type of traffic since.