Tripac Apu issue

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by ryan730, Nov 16, 2019.

  1. ryan730

    ryan730 Bobtail Member

    Jul 22, 2015
    Not sure where to post this, but I figure this is as good of spot as any.

    Having an issue with my Tripac Apu and it not wanting to start.

    If the controller is set to A/C the Tripac will fire up without an issue.

    If the controller is set to Heat and/or Fan the Apu will start intermittently. When it does not start, it will go through the buzzing, clicking of the fuel pump and then turn over literally what sounds like once and then try again in a minute. No error codes register.

    How can the unit start and crank over and turn on when set to A/C but when it’s set to heat/fan it will intermittently fail? It sucks to wake up to dead batteries and it’s making me idle in cold weather.

    Please point me in the correct direction of what to check because normal things like belts, alternator, fuel pump, filters, etc shouldn’t be an issue as it was just serviced.

    I did need to have the relay board replaced due to a bad solder point, could that cause this issue?

    Anyhow thanks in advance!
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  2. Tx Countryboy

    Tx Countryboy Road Train Member

    Sep 18, 2019
    Heater valves open under hood of truck.
    PE_Trans and A5¢ Thank this.
  3. ryan730

    ryan730 Bobtail Member

    Jul 22, 2015
    Yes. Not getting an eng code when it fails to start.
  4. Dave_in_AZ

    Dave_in_AZ Road Train Member

    May 4, 2015
    I'd say yes on a relay. Sounds like something is stuck, telling it to shut off, when something is telling it to turn on.

    I have 2 trip pacs.

    You could check the fuses under the cover wear the reset button is.

    There are about 10 fuses under that black cover.

    Going TK is hit or miss and very expensive.

    The guys at Glendale Laser Alignment in Phoenix are outstanding APU guys if you get by there.
    PE_Trans Thanks this.
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