I'm interested in swapping out the mechanical fan on my Volvo to an electric one. Today at the boneyard, I found a fan out of a Olds that I have read works well for this application. Anyway, this fan appears to be a two speed variety and has two relays connected to the wires going into the fan. From what I can tell from the three terminals coming out of the fan, there is a common ground and two positive terminals. When I connect of of them to the positive side of a 12V battery, the fan runs and draws about 8 amps. When I connect the other terminal to the hot side of the battery, the fan runs faster and draws about 12A. Interestingly enough, having both positive terminals connected to the battery didn't seem to make any difference in the output of the fan. I assume they made it this way so it can run at a set amount for cooling and then it goes into overdrive when the air conditioning kicks in, or vice versa.

What is going on here? Does having the "hotter" terminal connected somehow disable the lower amp drawing terminal? This is the main thing I'm interested in learning. I was thinking about wiring it so the fan would run when the a/c was on and then it could run at the higher setting when the thermoswitch in the radiator kicked in, or do I have this backwards?

Thanks.