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  1. #1
    Join Date
    Apr 2005
    Two Potential Relays were installed in this 3 door freezer and both potential relay coils burnt open. The compressor is a semi hermetic Copeland (208/230- 1phase) with start and run caps in the circuit. The cap’s measure good when tested and the compressor windings ohm out R to C = 1.4 ohms, C to S = 4.2 ohms, R to S = 5.3 ohms.
    This is an older Universal –Nolin 3 door reach in which ran well for the 1st hour after it was properly charged and dropped the temp 30f. It has no pressure controls just a thermostat which is new. I mention this because before both potential relay coils went open after it short cycled a few times. I don’t know why it short cycled because the thermostat contacts were closed. The Protector disc in the terminal box is also good and does not open until the coil burnt up and the potential relay contacts closed engaging the start windings. I don’t know what caused the potential relay coil to blow.
    Any advice would be greatly appreciated.

  2. #2
    Join Date
    May 2004
    To start with I would look for a hot leg and check for bad wiring.

    Second I would see if there was anything else on the same breaker.

    If everything shows ok and nothing else on the breaker I would look to see it you have the correct start components as stated OEM. If in question, put a s/s hard start kit on it.

    If that fails, I would question your compressor windings.

  3. #3
    Join Date
    Mar 2005
    I agree ,check the components being used against the oem,s listing to see if your using the correct ones.Also check the running amps to make sure your not over amping.Also I feel you should never change the relay without also changing the start cap.To me thats like changing one sock!!!.Last thing I would do is meg the windings. Good Luck.

  4. #4
    Join Date
    Dec 2002
    If the pickup voltage generated by back EMF is above the maximum, the relay coil stands a good chance to overheat and open circuit. In addition, potential relays also have a continuous coil voltage rating. This is the maximum back EMF that the relay’s coil can tolerate continuously without overheating and opening circuit.Then the contacts between 1 and 2 would stay closed, causing high amp draw and trip the overload..hopefully!

    [Edited by shogun8 on 04-23-2005 at 04:52 PM]

  5. #5
    Join Date
    May 2000
    Monmouth Junction-NJ-USA
    Definiteyly check the components against the compessor model. A lot of copelands use Current Relays.
    If you really know how it works, you have an execellent chance of fixin' er up!

    Tomorrow is promised to no one...

  6. #6
    Originally posted by rayr
    Definiteyly check the components against the compessor model. A lot of copelands use Current Relays.
    Ok ... lets begin with how OLD THIS SUCKER IS...

    what does it cound like when it's online?

    You say it cycles off and on again.
    Find out WHAT it is cycling on ... the Klizon perhaps?
    Maybe you have bad bearings and once the unit runs for awhile ... it gets bogged down and that kicks back in the start relay. And there goes the on/off cycle.

    If you have power to the compressor within the range it was meant to operate at... for example: an older style K body with the electrical configuration CAB ...would be wanting to find 230 to 250 volts ac, single phase.
    And the never models have CAV which is meant to accept voltage as low as 195 and run on up to 240 volts, single phase.

    In the old systems, we had to install buck and boost Acme transformers to elevate 208 to 230.
    The systems simply WOULD NOT run on the lower line voltages.

    If the system is starting with the voltage you got coming in ... then your voltage probably is NOT your main problem here.

    It is either your relay is sensing an overcurrent condition which means it feels the armature is slowing down... so the relay comes back into the circuit.
    Or your Klixon is opening up due to some othe cause of over-amping.

    Maybe the box is a freezer and the valve in the suction line is not adjusted properly.

    Monitor your voltages and amp draw during the run.
    Check for a lose connection at the compressor terminal board!
    Had one which drove two of us nuts for an hour.
    Just a lose connection.

  7. #7
    If you opened the potential relay, and physically saw that the coil is burnt, this is only due to over voltage going to the coil. Its cause could be an open run capacitor or wrong run capacitor or wrong potential relay. Measure voltage from #5 to #2 when the compressor is running and make sure your relay is rated for that voltage. Check power supply to unit to make sure your not operating on voltage higher than 130 volts. Check the oem’s specs for starting components.

  8. #8
    Join Date
    Feb 2004
    northern colorado

    I have had something close to your problem

    I had a call on a six door freezer not working. I found that the start components had failed,replaced them and started it all back up. All looked fine. Two weeks later got another call on the same freezer, this time lost the compressor to open winding. Change out the comp and all electrical components. Less than two months later another call, this time the start components failed.
    All this happened shortly after startup. I decided to check out the electric supply to the unit by meging out the lines to the unit, but all looked good. Then I checked the service to the building. The service was rated for 3oo amps, found the current at 292 amps and the three gas paks were not running, and each of those are five tons each. The building did not have enough service.
    Check your service to the building and do a load calc.

  9. #9
    Join Date
    Apr 2005
    This was my first post and i'm very impressed with the great information that was given back to me. I wiil take all this advise and and work with it until the puzzle is solved. Additional info: The Klixon switch has been bypassed for the fact the customer is using this freezer only as a frigerator. The CPR valve has been removed for an unknown reason. The copeland compressor is a CAV model. The potential relay was purchased by copelands compressor model number. Thank you to everyone's help and i will post updates as i perform additional work to the unit.

  10. #10
    Join Date
    Apr 2005

    start relay problem

    I had a similar problem with a newer copeland k body and after some research found that there were in fact two acceptible relays for this particular compressor. Each relay has a different pick-up and drop-out voltage as well as constant coil voltage ratings. This info on the relays came straight fom the factory warranty dept. of True.

  11. #11
    Join Date
    Dec 2000
    Flat Rock, NC
    The start components are failing due to the removal of your cpr valve. This valve prevents overloading the compressor after defrost and during start-up after long off cycles. The fact that its now a cooler greatly increases the load on the compressor. The compressor cannot maintain full rpm when overloaded causing potentail relay voltage to fall, letting start relay kick back in and causing rapid cycling of start relay. This will cause rapid coil and capacitor failure. Also the start winding will overheat and burn out.

  12. #12
    Join Date
    Feb 2005
    I have worked on a few of those lets see, mars 67 or 040-0001, 20x440 run and 130/156 330vac start, kalb-150-cav or cab.

    [Edited by jimp on 04-29-2005 at 09:45 PM]

  13. #13
    I like what you said about getting good straight advice here.
    That is part of what we are all about.

    Now here is some more.

    Your employer's customer is cheating themselves!
    They are demanding this freezer perform outside of it's designed range!

    A freezer is not supposed to work as a cooler and a cooler is not supposed to work as a freezer!

    There's not one guy here who is worth their salt ... that has not pulled some stunt like "converting over" a freezer to a cooler.
    Bad move.
    Not good idea.
    It is a lose/ lose situation!

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