apu problem

What kind (make/model) of APU is this? Are you sure the APU is in "standby mode"? (Starts and runs when battery voltage drops below a set level) What all do you have running on the truck that's drawing power, if anything. Make sure no compartment lights stay on. You could have bad battery(s) that are essentially bad cells inside and are constantly discharging themselves.

 

What's the make and model of APU?
How long has it been sitting for? It's not unheard of for them to lose prime after sitting. Ensure the fuel filter is on tight and all fuel lines are connected and snug. These don't sit and crank continually - it's a brief attempt, the control module bases whether it was successful or not depending on if it reads output from the alternator, then it tries to crank again... typically, five time before it quits, then it needs to be reset before it'll try to crank again.

 

At the bottom of your bunk is there a yellow or red light blinking? Count those blinks (2 pause 4 equals 24). That's an alarm code. Download the manual (Google finds it quickly IE: Thermo King APU codes) and look up the code.

Hope that helps a bit.

 

No problem. That code will cut down on repair time a lot, and it may just be something you can handle yourself.

You said it's a Tripac. On their standard install, they include a 3-way switch on the dash for starting a regeneration of the APU's DPF. If that switch has an amber light glowing, you need to do a regen. This is easy. Put the APU controls to standby mode (bunk controller). Now, with the truck running press up on that 3 way and hold it for about 30-45 seconds until the amber light starts to flash. Drive at highway speeds for the next 1-2 hours (1 is standard, really clogged is 2 hrs). This will turn on a burner in the APU's DPF to clean the filter. It draws a bit of electricity so it's best to do this with your headlights off.

You can also Force a regen, even if the amber light is off. To do this, hold that switch for about 1 minute until the amber light comes on. Then release it and again hold it until the light starts flashing. I used to force a regen every 3 days or just before I'd be taking a reset. A TK service tech taught me that so I wouldn't get regen alerts during resets.

 

This light you speak of, is it on the power inverter? When my power gets low enough that thing starts beeping and it does have a light on it but, I just assumed it is for the low voltage to the inverter itself? Other than that, I don't see any other light. My control panel has codes and what not but the only code I ever see is the low battery code, after the APU won't start , or tries to start and won't start.

 

he might have the old tri pac without dpf. have you checked the circuit breaker on the fuse panel located inside your side box. i have same trk with an a tri pac. if it fails to start and control panel says eng with red fault light the circuit breaker has popped, it's resetable just by pushing back in with control panel off. also under drivers step in battery box check connections for corrosion. bet you will find the t/a didn't check connections or load test batteries. pull all the connections and clean with baking soda and coat with dielectric grease. while your at it load test the individual batteries with a load tester while they are disconnected. just find the cca listed on batt and enter into load tester. bet you will find a bad battery. one last thing before apu attempts to start do you hear the preheat buzzer?. and electric fuel pump start running like 2-4 seconds before apu start to crank?. if not inside fuse box compartment usually in pass side box pull cover and check the preheat fuse and fuel pump fuse one might be blown. good luck.