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  1. #1
    Join Date
    Jan 2011
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    USA
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    A/C Compressor will not start


    Hello All,

    I am new to your forum. My first thread. Hope some of you guys can help me out on this problem.

    Sorry for the long-winded message, but trying to bring you up-to-date on where I am on this.

    I had a tech come out and check my AC, BTW, which he installed a new compressor a year ago. The compressor will not start now. It was kicking out the breaker (30 amp). He said I needed a new breaker (50 Amp)(that's all he checked). I installed a 40 amp as I thought maybe a 50 was to large for my 5 ton unit. It does not trip the breaker now but the compressor still will not start. It hums for 3-5 seconds and clicks off.

    I have checked the capacitor and it checked OK, I replaced it anyway and got the same results, no start. BTW I have not called the tech back yet, he seems so sure there is no problem with the compresser motor (all that is still under warrenty).

    I have checked the wiring connections and all seem normal except the 3-wire plug on the compressor and it shown signs of rust/corrision, which I clean up and checked with my meter and it appears to be OK.

    The capacitor is a dual run type. One for the coil fan and one for the compressor. When I check the volts on each terminal of the cap, including the common, I have 120 volts on all 3 with nothing running. When I try to start, the fan shows 350 volts and the compresser cap terminal still shows 120 volts with no increase when compresser "hums" trying to start.

    I checked for a short internally and "open" in the motor, but it seems to show none, at least to me. The ohm reading across all wires to the compresser show less than 2 except for one and it shows 2.4 ohms.

    Is the "run" wire from the capacitor to the motor and fan supposed to show 120 volts when system is not in run position?

    The contact switch, Red wire side from incoming power has direct path (metal strip) to compresser red wire side. The incoming Black wire has a contact point which engages when "run" is attempted, but when system is down, this black wire to the compresser has 120 volts constantly with contact points open, IS THIS NORMAL? The Black wire from the motor appears to be getting the 120 volts from the red wire's 120 volts into the motor. Is this normal?

    If you need any more info or do more tests, I'll be glad to do my best.

    Thanks and Have a Great Day,
    jraquel



  2. #2
    Join Date
    Dec 2010
    Location
    Ireland
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    Re: A/C Compressor will not start

    Sounds like your compressor is seized. The unit was trying to start and was tripping out the smaller breaker. Must be just falling short on tripping out the larger one.
    50amps is far too large for that unit. Firstly the breaker should be motor rated to allow for starting currents but should not need anymore than a 20-25amp breaker.
    You could check the resistance across your windings to determine whether one of them is damaged.
    You will get power to your run winding on startup but your start winding should drop out once a certain compressor speed is reached.

    One of your fellow countrymen would probably be better to answer the other aspects of your question relating to power

  3. #3
    Join Date
    Feb 2009
    Location
    Australia
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    Re: A/C Compressor will not start

    Bigfreeze,,,remember US is 110 volts
    Remember we are here for a good time, not a long time.
    Trust me i'm a Fridgy.

  4. #4
    Join Date
    Dec 2010
    Location
    Ireland
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    Re: A/C Compressor will not start

    Quote Originally Posted by lawrence1 View Post
    Bigfreeze,,,remember US is 110 volts

    Realised that after the post was made.

  5. #5
    Join Date
    Aug 2006
    Location
    england
    Age
    40
    Posts
    3,463
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    27

    Re: A/C Compressor will not start

    Be carefull doing too much yourself, many techs will not honour a warranty if third parties have carried out work that may have led to the failure, such as in your case replacing compressor start capacitors.

    It does sound like your compressor or possibly the wiring harness to it is faulty.
    The 120v on all wire when off is due to the fact that the contactor/relay in your unit only switches one of the lives feeding the unit, i expect there is 240v across the red and black wires and 120v from each wire to ground, this needs checking just to be sure the compressor is getting the correct power it needs to run.

  6. #6
    Join Date
    May 2006
    Location
    Sussex
    Posts
    343
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    9

    A/C Compressor looks defective

    If you are near the end of your 1year warranty, I suggest you write him a letter to record that you reported the breakdown on (date) and that you believe the fault to be a defective compressor, which is within it's warranty period. (Don't say anything about changing capcitors etc.)

    If this drags on until after the warranty date expires, and only then gets reported to the manufacturer, the tech will have trouble getting the manufacturer to cover the warranty and will then want to argue with you about it.

    Get the tech to repair the thing and keep him responsible for it running again. Changing a breaker and it still does not run is not the end of repairs and not the product you want.

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