Volvo manual fan switch

On some of the Youtube trucker videos I like to watch they sometimes switch on their fan manually to allow more control of their engine temperatures. My Volvo VNL780 doesn't have this feature. In fact, I've never seen a Volvo (in person or pictures) that had a fan switch. Does Volvo feel they are not needed? Maybe they are not, but I think it would be cool to have. Could it be done? I decided to do some research to answer that question.

The fan clutch is controlled by air. When air is applied to the clutch it is disengaged and the fan doesn't run. Dumping the air in the circuit applies the fan clutch and the fan. In case of an air leak or air loss the fan defaults to being on as a safety feature.

A fan switch can be added mechanically by placing an air solenoid in the air line to the fan clutch. You flick a switch and dump the air to engage the clutch. I didn't like this idea of hacking into the factory air line. I prefer to keep things as 'factory' as possible...especially where air lines are concerned.

The factory uses an electric air solenoid to engage the fan. You can piggyback a switch onto this circuit to operate the fan, but according to my research this will cause the truck computer to display an error code. I don't want that.

This link gave me two less invasive ways to electrically engage the fan via factory wiring. I have a Cummins ISX 870. According to Cummins Insite documentation I can apply the fan by connecting pin 34 to pin 17 of the engine control harness. I wasn't sure how to cleanly do this since the connector is exposed to the weather. You also have to have the feature enabled in software. That part sounded like a lot of effort.


The second method, and the method I chose, was to enable the fan through the Volvo VECU by applying 12V to pin PA-19. PA-19 is the empty spot shown by the arrow on the green connector. This mod is supposed to work no matter what engine type...Volvo or Cummins. The VECU is relatively easy to get to. Just lift the fuse block out of the way.


The official Volvo pin for this connector is P/N 3948725. I couldn't find this connector online and I didn't want to go through the hassle of ordering from a Volvo dealer, so I tinned about 1" of wire and stuck it down the slot. The way the connector is made it won't contact other pins. The wire was very snug when it slid down beside the pin, so I have no fears of it falling out.

I fired up the truck, let the air come up, and applied 12V to the wire. The fan came on along with a small burst of air! A successful project that cost nothing.



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