2001 Peterbilt ac help!

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Salteedogg, Jun 17, 2021.

  1. Salteedogg

    Salteedogg Bobtail Member

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    Jan 18, 2018
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    Ok truck has been sitting for 3 years, the pressure was about 10 psi so decided not to evacuate it and instead just charge it, the first 2 cans of r134 took it, also the compressor started cycling on at about 2 times per second. So as the compressor is cycling, it’s stuck on 90 psi low side, pressure not moving when it cycles. The high side is around 150 psi. It would not take a 3rd can. I jumped the sensors and nothing changed, even made sure the trucks fan was blowing. I also checked voltage at compressor which is a constant 12 volts. Is my compressor shot considering it has a constant 12 volts, which should keep it on without cycling?? Or does this sound like an orfice tube problem. Don’t want to throw money at it. Any help is GREATLY appreciated “
     
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  3. BoxCarKidd

    BoxCarKidd Road Train Member

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    If you have 12 volts to clutch and a test light will not light on the ground ground side, indicating a bad ground, it should be engaged.
    I worked on a Ford with a low voltage alt. It would work on and off again but not cycle like that. Clutch air gap should be checked. Never saw that cause cycling as well.
     
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  4. Salteedogg

    Salteedogg Bobtail Member

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    Jan 18, 2018
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    Yeah checking the plug going to compressor, it’s holding a steady 12 volts, no drop in voltage!
     
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  5. Rideandrepair

    Rideandrepair Road Train Member

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    I totally understand not wanting to throw money at it. But when it comes to A/C on a Truck. The choices are to replace parts, or pay a Shop. Given the amount of use they get. Any money spent is well spent, since something else will just fail anyways. Every year it’s something. For that reason I often replace only what’s needed. Only time that hasn’t been true, is after replacing everything. Then it’s 3-4 yrs at best, before something gives. The orifice on those are often a problem.I think I’d first blow the system out with regular compressed air..Nitrogen if you prefer. Replace both orifices with new ones. New dryer, maybe add an Oz or 2 of oil w/ dye in for good luck, pull a vacuum.if possible. Then try charging it. I would rather also put a new compressor on it along with pressure and fan switch. Keeping old ones as spares for future diagnosis, or emergencies.Since if this compressor goes bad, it might contaminate your new orifice and dryer, along with the condensor and maybe the evaporators Money well spent. If it’s a York compressor, good chance the clutch is bad. If it’s getting real hot, and cycling off, good sign the clutch is no good. The heat often burns the compressor bearing out along with it, but the York clutch is easy to change. Sanden compressors a different story. Not worth changing. A new compressor can be had for slightly more $$ anyway. Either way usually not worth changing a clutch. I’ve done about 4-5 on York’s. Only to have the compressor go bad soon after anyway. Only maybe twice was it worthwhile. If I recall correctly equal pressures while charging, shows compressors bad. Compressor must be running of course, equal pressure shows it’s not compressing, even though it’s running. I’d guess the blocked orifice is keeping it from taking Freon and keeping compressor from running, Till it’s running, you’ll never know if it’s compressing. I’m not a tech, but have done my own for 20+ yrs. Only time it hasn’t taken Freon, or has been real slow is when my expansion valve(s) were bad.That was after going 2 yrs without A/C, when I swapped from a York to a Sanden. Everything flushed and new. Trouble free for 3 yrs. now. Except for a couple minor leaks I’ve repaired. Loose line, Bad Shrader valve. Nothing major.
     
    Last edited: Jun 19, 2021
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