Dual Electric Fans on Carb'd Engine

[ProServ]

Old thread but in case this helps anyone else.

You could stagger each fan as you mentioned or you could wire the fans like GM often wires the dual fan vehicles so the two fans come in staggered, both a low speed initially and then both at high speed.

First the two fans come on at low speed (series wiring) and then at a higher temperature they both go to full speed (parallel wiring). You would need two temperature switches and three relays or you can use a temperature based relay controller with a single temperature sensor (but you still need a harness with three relays).

Look at page 6 of this document for an example of how this would be wired.


BTW - the product in the above instructions could also be used to do the staggered (full speed fan 1, then full speed fan 2) control you also mentioned.

Originally Posted by Neil B

Hey guys, I've got twin Spal fans that pull some serious amps when they kick on. I currently have both fans on a single 185 degree sender. The problem is that the load from these fans causes idle speed to drop about 300 rpm. If I get my 'fans off' idle speed and mixture where I want it, the engine will stall when the fans start. This is a carbureted engine and I really don't want to add complexity with any type of IAC solenoid or PWM fan controller. I am considering either wiring 1 fan to key on ignition (always on) and then having the other fan come on at 185 degrees via the sender. Or, I could run 2 senders and stagger the fans to 185 and 195 degrees, but I think I would still have to run a higher 'all fans off' idle speed. Thoughts?