apu cooling fan

If it's anything like most electric fan systems, a cooling temp sensor sends a signal to the ECM which in turn energizes a relay that turns the fan on.

Many times the cooling temp sensor or relay goes bad.

What APU do you have and what code is it throwing??

 

I'm not savy on tripac's. I know a little, but not a whole bunch.

Temp sensor is usually near the thermostat housing or in the head.

There are relays under the bunk with the rest of the controls.

It seems to me I seen a relay in the engine compartment before protected with foam rubber. Follow the wires off the fan should lead to the relay. The relay has to be fairly close because of the wire size. I doubt that one is in the truck, but in the engine compartment protected from the elements with something.

Another thing, it could be the fan itself. Unplug it and run direct 12V jumper wires to it and see if it comes on.

There's a tripac technician that works on justanswer.com. But they charge for answers. Like $5-15 an answer.

Here's a link to him if you want. His name is Wayne.

http://www.justanswer.com/heavy-equipment/4s60e-thermoking-tripac-recently-brought.html

 

Did you ever get it resolved? I have yet to see my radiator fan kick on and today in scorching Phoenix heat the apu shut off with engine code light up.