So I have a Tri-pac APU on my truck. Twice now I have had issues this week with a hot-soak shut down restart issue. (Hot soak is where you shut it down for a short period of time and try to restart it.)

In both cases it's been over 90 degrees outside too.

The first time, never knew it shut down as I went in to shower and eat and when I came back out, there was an "ENG" system fault. Tonight I was still in the truck. And when it's 93 degrees out and you want AC, you figure this stuff out.

I went searching for the Tri-PAC maintenance manual some months ago and found one. I'd upload it, but it's 6.5 MEG, so unless the site is willing to host it, Google is your friend.


You first need to turn your APU off.

Start your truck and let it idle for about 5-10 minutes.

Reset the APU "Engine Reset Switch" It's on the control unit. Who knows where they installed it on your specific truck.

Shut down the truck.

Turn your APU on.

Enjoy your AC.


near as I can tell, the Coolant gets too hot in the APU engine and sets an overheat condition. I need to talk to our mechanic, to me, that sounds like there's a waterpump problem on the APU. It should flow the coolant when it restarts to clear it. I do know running the truck engine for 5-10 minutes seems to cool it off and then it will run no problems the rest of the night.