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Thread: A/c

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    A/c

    2000 Peterbilt.
    Sometimes the air blows cold sometimes
    It dont. The compressor kicks in as normal when it's cold when hot it's not working. Added some 134 to it but it hasn't made a difference.
    Does anyone have a clue besides replacing everything?
    Thanks


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    "The Legend" REDD's Avatar
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    Compressor going bad? To much R134? Not enough R134?

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    According to one who hooked gauges up it had enough.
    How do ya know if compressor is bad? Who's to say it's not a switch or something? Is there a way to test compressor

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    Road Train Member Rerun8963's Avatar
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    Quote Originally Posted by jaysolomon View Post
    2000 Peterbilt.
    Sometimes the air blows cold sometimes
    It dont. The compressor kicks in as normal when it's cold when hot it's not working. Added some 134 to it but it hasn't made a difference.
    Does anyone have a clue besides replacing everything?
    Thanks
    Quote Originally Posted by jaysolomon View Post
    According to one who hooked gauges up it had enough.
    How do ya know if compressor is bad? Who's to say it's not a switch or something? Is there a way to test compressor
    sounds like something internally is freezing up, like a valve. i would highly recommend a flushing of the system which would be best done at a place that does A/C repairs. as far as making the compressor run, the plug on the compressor can be "jumped" for testing. but this is why i am leaning towards something freezing. at one time, the system must have been opened up for repairs, and not properly evacuated. evacuation removes all the moisture from the system when it is opened up, and the humidity in the air gets in. at one time a CCOT valve, located in the evaporator inlet was a huge culprit for freezing up. when the A/C is turned on, look for frost around the system, frost will be the indication that right there is a blockage and its freezing. i would NOT recommend by-passing the compressor, if you do and the blockage backs up the freon, you stand the chance of blowing out the compressor. the first thing i would recommend replacing (after the flushing) is the "receiver-drier" or sometimes called the "accumulator" which is much like a filtering device that has a desiccant inside. if it trapped moisture, it is toast now.

    on another note, if the system has never been opened up for earlier repairs, you may have a leak, which is also sucking in air/humidity. you may also have a low oil level in the system as well. this is when an evacuation of the system will show you that you may have a leak, as it will not hold a vacuum. look for traces of dirty connections (indicating the leak with oil around it), and even chaffed hoses.

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    The system has never been opened up. I have noticed the lines are real wet.

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    Also systems use an expansion valve....it can get plugged/fail...resulting in failure or odd operation...

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  9. #7
    Road Train Member Rerun8963's Avatar
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    Quote Originally Posted by jaysolomon View Post
    The system has never been opened up. I have noticed the lines are real wet.
    the lines will be wet as the frost melts.

    then there can be a slight leak. for the past several years, when we turn on our defrosters or on some dash panels defoggers, the a/c compressor comes on. this is to "de-humidify" the air in the cab, which is where the fog on the inside of the window comes from. the manufactures had done this also so that the compressor gets used during the winter months, allowing for the front compressor seal to be lubricated. back in the "olden days" we did not use the a/c in the winter, but it was recommended to turn it on if only briefly to lubricate that front seal. but who actually had done that..?? this cause a bad leak at the compressor seal, and thusly the R-12 (back then) to escape.

    you having a much more modern system, need not cycle the a/c during the winter, it's done automatically, however, any a/c system is still prone to leaks, and on a big truck, all the vibrations in a years time will indeed shake something loose.

    you will have to look for dirty connections which i mentioned in another posting. those indicate a leak. it may be something as simple as a loose connection that you can tighten up. also too, your radiator fan is supposed to be on any time the a/c is turned on. i would check to make sure your cooling fan is working. also check to make sure the condenser is free of any bugs, debris. if you have a sleeper berth, you must check the evaporator under the bunk. it can be clogged up with dust. maybe something is blocking the airflow like a rag or blanket, or some other object. if you take along a pet, pet hair will certainly clog it up too. check the a/c lines that got from the front of the truck to the sleeper (if you have a sleeper)



    Quote Originally Posted by ZippyNH View Post
    Also systems use an expansion valve....it can get plugged/fail...resulting in failure or odd operation...
    expansion valve, that's it....for the life of me the name of some of the parts escaped me...thanks for "the jog"....

  10. #8
    Yup
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    sounds high pressure switch
    Whens the last time you cleaned the filters ?
    No not the inline dryer filter,the ones under the dash and under the bunk.

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    Cleaned filters 2 weeks ago.
    According to Peterbilt it has a expansion valve for the bunk and an orphis for cab.

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    Road Train Member Rerun8963's Avatar
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    Quote Originally Posted by jaysolomon View Post
    Cleaned filters 2 weeks ago.
    According to Peterbilt it has a expansion valve for the bunk and an orphis for cab.
    the orifice tube clogs up. sometimes material from the receiver/drier (desiccant) breaks up and starts floating in the system (which means you will need a new receiver/drier, they DO NOT have a long care free life, they DO expire). a flushing "might help" you, but then again more of the desiccant can break away. it's also possible that the refrigerant oil has gelled up (although it should not) and that can be clogging the orifice tube.

    we can be here all day/night diagnosing your problem. take it to a shop.

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    Yup

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