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  1. #1
    Join Date
    Jan 2013
    Location
    Oregon
    Posts
    25

    Danfoss 1/4HP Compressor

    Im looking at a Walk-in cooler condensing unit that has a Danfoss 1/4hp compressor. The condensing unit is outside and the crankcase heater blew. It took out the contactor and starter relay as well. I took the bad crankcase heater out of the sytem, replaced the blown components and ohmed out the compressor. The compressor at first ohmed out ok and didnt have winding to ground shorts. upon restarting the compressor drew nearly 100amps and trips breaker and wont start. I thoroughly checked everything in the condenser unit, defrost timer control, start and run capacitors, pressure controls, guages show equalized refrigerant pressure in system, I checked fuses and connections in disconnect box, the breaker in main panel passed continuity check. based on the amp draw and failure to start, I'd have to assume the compressor is bad. once when ohming the windings my meter bounced around a little before confirming continuity. Can compressors be borderline bad to the point where i dont get a definitive winding-to-winding or a winding-to-ground short? I had a Clamp-on meter on the common winding at the load-side of the contactor and a clamp-on meter on the start relay/start capacitor. The meter at the contactor got the high amps and the meter on the start circuit looked like power wasn't even making it to the start capacitor. Is it safe to assume the compressor is bad? Thanks for any feedback.

  2. #2
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,575
    the crankcase heater blew
    Not sure what this means, but I find it hard to believe this took out the contactor and start relay. The heater should be on the line side of the contactor and the relay on the load side. Methinks the compressor or relay was bad and one took the other out. and the cch "blew" as a fluke
    Officially, Down for the count

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  3. #3
    Join Date
    Jan 2013
    Location
    Oregon
    Posts
    25

    relay/compressor

    Quote Originally Posted by 2sac View Post
    Not sure what this means, but I find it hard to believe this took out the contactor and start relay. The heater should be on the line side of the contactor and the relay on the load side. Methinks the compressor or relay was bad and one took the other out. and the cch "blew" as a fluke
    It doesn't necessarily matter which took out which, they were bad and i replaced them. My main question was can compressor windings be bad but yet not give a definitve open winding when ohmed out? Is it safe to assume that the compressor is bad based on failing to start and drawing high amps (after replacing and checking all the other compionents)?

  4. #4
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,575
    Yes. For a unit that small, a compressor analyzer would have given you an answer in a couple minutes if the pump was bad or not.
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  5. #5
    Join Date
    Jan 2013
    Location
    Oregon
    Posts
    25

    compressor analyzer

    Quote Originally Posted by 2sac View Post
    Yes. For a unit that small, a compressor analyzer would have given you an answer in a couple minutes if the pump was bad or not.
    Thanks. I appreciate your input. Ill look into getting a compressor analyzer. I've only been using a meter to check compressors.

  6. #6
    Join Date
    Oct 2009
    Location
    Raleigh, NC
    Posts
    794
    Are you sure a walk-in has only a 1/4 hp compressor?

  7. #7
    Join Date
    Nov 2012
    Location
    MI
    Posts
    5
    Did you only check continuity? What did each leg ohm out at? 1/4hp seems small for a walk in, 100 LRA seems high for a 1/4hp anything.

  8. #8
    Join Date
    Jan 2013
    Location
    Oregon
    Posts
    25
    Quote Originally Posted by oyader View Post
    Did you only check continuity? What did each leg ohm out at? 1/4hp seems small for a walk in, 100 LRA seems high for a 1/4hp anything.
    The Common to Start winding was 2.1 ohms, the common to Run was .7 ohms. Run to Common was 2.8,2.9..The Run winding bounced around some each time I ohmed it out. The rated RLA was 24Amps. I cant remember what the rated Locked Rotor Amperage was, maybe 80something.. Its a 404A system.

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