A/C repair question

Discussion in 'Trucks [ Eighteen Wheelers ]' started by IowaDoorSwinger, Jun 7, 2024.

  1. IowaDoorSwinger

    IowaDoorSwinger Bobtail Member

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    Jun 7, 2024
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    I replaced most of the a/c system. the clutch on the compressor was not kicking in and was losing refrigerant somewhere around expansion valve. Replaced compressor, dryer/filter, high and low, switches, and expansion valves. Finally got it to hold vacuum for an hour, no psi lost. Charged the system back up to spec. Watching the guauges on the manifold when truck is running, the low side is about 32 psi but the high side will run all the way up to 450 before I shut it off or manually turn on the engine fan, then it will drop back to 150psi. Also the gauge on the high side will start fluttering above 300 psi. A/C is blowing about 55 degrees now.

    Could there be a problem or blockage in the condenser? And shouldn't the fan kick on at 300psi?
     
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  3. Big Road Skateboard

    Big Road Skateboard Road Train Member

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    Yeah, fan should kick on 300-325.
     
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  4. IowaDoorSwinger

    IowaDoorSwinger Bobtail Member

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    that's what I thought. the pressure switches are both new, but they came from Napa. wondering if I should make the 150 mile round trip to the dealer and get OEM.
     
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  5. Big Road Skateboard

    Big Road Skateboard Road Train Member

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    What truck? How did they look up the part #'s
     
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  6. IowaDoorSwinger

    IowaDoorSwinger Bobtail Member

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    Jun 7, 2024
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    I brought the old switches with me and matched them up. that's the only way they can do it. my F/L dealer gets a little schitty about giving out part numbers if he knows your not going to buy from him
     
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  7. IowaDoorSwinger

    IowaDoorSwinger Bobtail Member

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    Jun 7, 2024
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    forgot. Its a '15 wester star 4900sb
     
  8. Rideandrepair

    Rideandrepair Road Train Member

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    Fan should be coming in as you said. Make sure the switches you bought are hi and lo switches, not hi/lo switch and a fan switch. Any parts book or counter can tell you the fan switch spec. Might find a catalog online at Truck air .com. Assuming it blows cold with fan manually engaged. I’m only guessing, must be a separate fan switch that’s bad. Find the fan air solenoid. Follow the air line from the fan. I’d be looking for wires running to the fan solenoid. Follow them to find the fan switch. Inspect the wires and plugs while you’re at it.
     
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  9. 5UG

    5UG Light Load Member

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    May 22, 2024
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    I wouldn't bother with that trip. Try unplugging the high side pressure switch. The compressor should go off. If it does, the switch is probably bad, or not getting a good read due to a blockage before the pressure switch. Run your hand along the high side and feel for any cold spots before the expansion valve. Cold spots indicate a restriction. **Warning: the high side lines get hot in general, but extremely hot at high PSI. You may want to use an infrared thermometer instead of your hands.
    Let us know what you find, and we'll go from there!

    Regards,
    5UG
     
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