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  1. #1
    Join Date
    Oct 2001
    Location
    Vancouver Island BC Canada
    Posts
    152

    Confused Carrier RTU 50 QD Series

    I having problems with the primary side of the control transformer blowing after about a one minute delay
    Main 60 amp line fuses are good. Checked and eliminated all possible and potential causes that I can see. Its 3 phase supply power, indoor fan motor is not single phasing equal amps and volts, compressors were ohmed and checked to ground, one or both of crankcase heaters was thought to have been the problem as I disconnected them during the troubleshooting and finally got the unit to run. I protected the primary side of the transformer with inline .5 amp fuses, however when I returned the fuses where blown again. I then changed the two contactors that are the pickup points for the power supply from the fuse block and once again the fuses blew.

    This ones got me stumped. I meeting an electrician on site to help prove proper, stable main power

  2. #2
    Join Date
    Oct 2004
    Posts
    31
    You are most likely experiencing an either constant or intermittant transformer secondary short/shorted load, wire, transformer winding,....etc.

    You need to check your control circuit..not everything else. What's the transformer doing? What's it's loads?

    What's the VA rating of your transformer? What's the primary and secondary current drawn?

  3. #3
    Join Date
    Jan 2007
    Location
    Milwaukee Wisconsin
    Posts
    984
    Quote Originally Posted by eastcreek View Post
    You are most likely experiencing an either constant or intermittant transformer secondary short/shorted load, wire, transformer winding,....etc.

    You need to check your control circuit..not everything else. What's the transformer doing? What's it's loads?

    What's the VA rating of your transformer? What's the primary and secondary current drawn?
    I Agree! The problem is with the secondary! Measure amp draw on secondary. Check VA of transformer & divide sec. voltage = Max amp.s of secondary

  4. #4
    Join Date
    Jan 2007
    Location
    Milwaukee Wisconsin
    Posts
    984
    Problems with the secondary, (shorts, loads, connections) often burn out the primary because of gage of wire & inductive reactance.

  5. #5
    Join Date
    Oct 2001
    Location
    Vancouver Island BC Canada
    Posts
    152

    Smile

    Thanks to those who responded and yes indeed it was on the secondary side. After proving the line voltage was stable and correct and armed with a handfull of .5 amp fuses . We proceeded to eliminated components starting at the low voltage terminal board and defrost control board. Finally found one of the defrost temp control switches to ground.
    With the low voltage fuse protection circiuit protection not opening that completely caught me and sent me off on the other direction.

    Love this job and if it was easy everyone would be doing it

  6. #6
    Join Date
    Jul 2003
    Location
    Orange County N.Y.
    Posts
    1,176
    Quote Originally Posted by JBocc View Post
    Thanks to those who responded and yes indeed it was on the secondary side. After proving the line voltage was stable and correct and armed with a handfull of .5 amp fuses . We proceeded to eliminated components starting at the low voltage terminal board and defrost control board. Finally found one of the defrost temp control switches to ground.
    With the low voltage fuse protection circiuit protection not opening that completely caught me and sent me off on the other direction.

    Love this job and if it was easy everyone would be doing it
    Next time you should hit up your local RadioShack for some .5 to 5 amp circuit breakers. I know that the ATC fuses are cheap but a little circuit breaker will last for years and is excellent for diagnosing problems like you had. Sometimes you can find them in a local supply house.

    ...Ron
    Roof Rat

  7. #7
    Join Date
    Dec 2006
    Location
    Canada
    Posts
    2

    Thumbs up

    You have a bad outdoor air econimizer! Disconnect the wires at the plug and manually open for fresh air till the new one arrives!






    "We stand on guard for thee" Canada

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