Old Air Products Dual Electric Fan Question.

[Mike_The_Grad]

I am installing old air dual electric fan setup for 67-72 c10. I got the components physically in the truck. I am at the wiring stage and I am a little hung up on how my specific setup is going to work. I do not have a/c (yet). The instructions show examples of several typical installations. All but one shows a/c compressors, trinary switches or pressure switches. I do not have any of these components. I will post pics of the instructions to show what I'm talking about. The kit includes 2 SPST 40 amp relays with a harness kit.(pretty nice actually) it also includes an adjustable thermostat with temp probe. (Rainbow electronics part# ts-120s)

Now, to my question. Based upon the pics provided and knowing I do not have any a/c components. If I wire this setup according to the "2 fans with a/c, without pressure switch with positive switched compressor" example but minus the compressor fan harness kit.

Will both fans run simultaneously as soon as ignition power is supplied?

Or will 1 kick on at the turn of the key, and the other kick on at the thermostat temp switch setting?

I would prefer to have one run anytime key is on while the other fan would kick on at say 220+. The thermostat switch range is from 32°F-248°F and is adjustable.

[VetteVet]

I see you've had no replies yet, but that isn't unusual on questions like yours as it takes awhile for someone with the experience in AC wiring to see what your asking.

The two diagrams I posted below show an easy way to wire the fans.
The first one shows how the fans would come on the normal way using
a t-stat switch and a trinary switch from the AC wiring. This setup would
allow the main fan to be controlled by the t-stat when it grounds the terminal
85 whenever the key is on. That is the normal way to run the main fan.
Positive power is applied when the key is on. but the fan won't run until the coolant temperature exceeds the preset value.
If you want it to run as soon as, and while the key is on, you simply need to ground the relay terminal 85 for the main fan.

Since you don't have a trinary switch you can use the AC relay with the variable T-stat, to kick on the AC fan.






This diagram is pretty much the same except it doesn't show the trinary switch but is just a normal relay. Both relays are run by the same T-stat and both will come on at the same time. If you ground the no. 85 terminal on the main fan relay and just run the AC relay off the variable T-stat you'll get the result you desire.





If I was wiring it up I'd use two separate T-stat sensors and have them turn on the fans about 10 degrees apart. Running a fan full time is not necessary and the AC fan may not be needed unless the AC is running a lot. Running the compressor is what heats up the engine coolant and at highway speed you'll get a lot of cooling off the incoming air.