engine-bay cooling fan operation Q

I answered my own question by doing a search

Out of curiosity what's the answer? I thought they both came on at once, though they're definitly different styles.

Normally one comes on when the coolant temperature rises above a certain threshold. The other comes on when the AC is switched on. Hmm, I wonder what happens in cars without AC...

John

The right one, the left one is wired to the AC circuit. The short search I did said that non-AC cars only had the one fan.

Those only have one fan...

Depends on the year the car was made. My 1983 900S only turns on the right-hand fan when the radiator thermoswitch cuts in. The left-hand fan only comes on when the A/C is on.

My 1985 900i is wired differently in that both fans come on together, then they turn off with the left one slightly delayed. I'm not sure if/when the wiring change was made or if it's part of the factory wiring or an after-sale modification.

I've seen a document on Tom Townsend's website about how to modify the fan control wiring so both of the fans in my 900S will run when the radiator thermoswitch cuts in so I'll be looking at doing that before summer comes around. It's winter here at the moment. 8-)

Craig.

It would be easy enough to add a second fan in cars without A/C if the owner wanted to add extra cooling.

Regards,

Craig.