Peterbilt a/c help

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Ashman_42, Jul 6, 2013.

  1. Lowboy456

    Lowboy456 Light Load Member

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    Mar 14, 2017
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    We have a 96 Pete 357 Dump that had great air when it was new but for years we havent been able to get it working good without it freezing.
    The blend door has been stuck on
    heat for years so we just shut the heater coil lines off under the hood in the summer.
    It turns out that the blend door being stuck on heat has been blocking the evaporator for years as it lays over and pretty much completely blocks the evaporator.
    I've got a blend door actuator ordered. And I'm hoping I can turn the heater lines back on and keep just enough heat near the evaporator to keep it from freezing. Along with charging it just enough to where the compressor cycles some.
    I have it charged like that now with the blend door manually moved to block the heater core.
     
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  3. Lowboy456

    Lowboy456 Light Load Member

    278
    128
    Mar 14, 2017
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    This is some very helpful info Gear Head!
    Our 96 Pete's 357 AC had been working great with one exception, it would freeze up and have to be shut off about every 20 minutes at the control panel to let the evaporator thaw out.
    Later the compressor failed and our mechanic put a new one on but didn't replace the dryer. The AC never was worth a darn with that compressor.

    Trying to get air working for our older driver, I took it on myself to evacuate the system and flush out the condensor and evaporator with denatured alcohol. During the flushing process I broke the suction line off the compressor because the metal fitting was fused to the male aluminum threads on the compressor.
    So now it has a new dryer, new compressor and is cooling decent thanks to this information. The compressor is cycling off ever so often and its working.
    It has a new fan and squirrel cage but does not seem to blow as hard as it did when the truck was new. There was a round foam strip near the squirrel cage to prevent air escaping the fan.
    That foam strip has deteriated completely and Peterbilt doesn't list it in their parts.
    I wonder if that could be the reason the fan doesn't move enough air?
    -----------------------------------------------------------------
    The 07 KW T800 truck that I drive arguably has the best air I have ever seen in a Heavy Truck. If my lazer temp is accurate I've seen 36 degree temps recently but have pics of it doing 39 degrees a couple years back with a Turkey thermometer.

    It has an expansion valve system. I have it charged to where the fan cycles on when the high side rises to 320 Psi.
    With the fan on, pressures are 25/150 until the high side rises and cuts the fan on.

    I don't think this compressor ever kicks off though unless the freeze switch at the evaporator is triggered, is this how it should run?

    Whoops! I see now that my previous post did go through and I can't edit it all down to one so I'll just keep this one like it is.
     
    Last edited: Aug 13, 2020
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