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PB ac problems

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Doberman83, Jul 29, 2025.

  1. Jul 29, 2025 #1
    Doberman83

    Doberman83 Bobtail Member

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    Nov 21, 2022
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    I’m working on a 2017 PB348 with a PX9 Paccar engine. The AC has been intermittently failing. Today I just happened to get the truck while the failure was occurring. No Ac, charge was good, had power to both pressure switches, no power to compressor coil. I checked the fuses and swapped the relay. I swapped the HVAC control panel with a known good one from another truck (PN Q21-6119) and the ac was working great. The driver took the truck to the job. When the driver returned he informed me that by the time he got to the job the AC had quit working. He left the truck off for approximately two hours and on the return trip (about 40 minutes) the AC quit working at about the halfway point. I did all of the same checks as this morning, fuses are good and I have power at both switches. Charge is good. I reinstalled the AC control panel that I removed this morning and everything works good.

    Is there something that could be causing this AC control to get hot or short out?
     
    Doberman83, Jul 29, 2025
    Doberman83, Jul 29, 2025
    #1
    singlescrewshaker Thanks this.
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  3. Jul 29, 2025 #2
    JB7

    JB7 Heavy Load Member

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    Dec 13, 2022
    Laurel, MD
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    "No Ac, charge was good, had power to both pressure switches, no power to compressor coil."
    Sounds like an issue with a switch. A few ways to check when it is not working. Remove the connector and use a jumper wire between the 2 terminals and see if that engages the compressor. Use either the continuity function on the meter if it has that or ohms to see if there is continuity. No meter sound or no ohms means no connection and the switch is bad. Make sure the connections at the switches and compressor are clean and tight. The best cleaner is DeOxit. Also a good idea to use silicone dielectric grease after cleaning. I would also closely check the wiring starting at the compressor and work your way back checking for chafing etc.
     
    JB7, Jul 29, 2025
    JB7, Jul 29, 2025
    #2
    singlescrewshaker Thanks this.
  4. Jul 30, 2025 #3
    singlescrewshaker

    singlescrewshaker Road Train Member

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    Dec 31, 2017
    Little Havana, FL
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    Possible weak compressor clutch?

    I chased that problem around all summer once

    Not sayn for sure that's your problem, but it was mine.
     
    singlescrewshaker, Jul 30, 2025
    singlescrewshaker, Jul 30, 2025
    #3
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