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  1. #1
    Join Date
    Feb 2011
    Location
    Fogelsville, Pa.
    Posts
    114

    How to force defrost? Carrier rtu. Pic of board

    I was wondering if I was missing something or is this board shot. In this pic on the bottom left there are two pins covered by a rubber cover. Dont I just jump these out to force defrost like other boards? Or do I have to take the wire from the 30 60 90 and place it on the jumper prongs? Maybe its just shot. I should be able to force it any time during the heat pump cycle, shouldnt I? Problem is its losing temp in side and the bottom(12inches) of the condsr coil is freezing up. I just recovered the ref and added the factory amount so ref. is good. Thx Its a Carrier Md# 50hjq005---501da

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  2. #2
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,619
    Defrost As frost builds up on the outdoor coil, the coil
    temperature drops below 28 F. When this outdoor-coil temperature
    drop is sensed by the defrost thermostat (DFT) and the defrost
    timer is at the end of a timed period (adjustable at 30, 50,
    90 minutes), the unit operates in a defrost cycle controlled by
    the defrost timer and thermostat. During this cycle, the reversing
    valve solenoid (RVS) is energized and the outdoor fan
    shuts off. The electric heaters (if installed) will be energized.
    The unit continues to defrost until the coil temperature as
    measured by DFT reaches 65 F, or the duration of defrost cycle
    completes a 10-minute period.
    At the end of the defrost cycle, the electric heaters (if installed)
    and the reversing valve will be deenergized, and the
    outdoor-fan motor will be energized. The unit will now operate
    in the heating mode.
    If the thermostat is satisfied during a defrost cycle, the unit
    will continue in the defrost mode until the time or temperature
    constraints are satisfied.




    looks like you need to jump the coil temp sensor out
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  3. #3
    Join Date
    Nov 2011
    Location
    USA
    Posts
    333
    Right...if the DFT is "closed" and the test pins are shunted, the board should "speed up" the timer and initiate a defrost cycle. But if frosting isn't uniform, there's usually something causing that (airflow/refrigerant flow), unless it "got behind" at some point, in which case they sometimes can't "catch up" without some "manual" assistance.

  4. #4
    Join Date
    Mar 2010
    Location
    Linden, Va
    Posts
    22
    Jump the sensor out then force a defrost. Make sure there is 24v on red coming into the board. If nothing happens. Replace the sensor and defrost board.

  5. #5
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,619
    well?
    It`s better to be silent and thought the fool; than speak and remove all doubt.

  6. #6
    Join Date
    Nov 2011
    Location
    USA
    Posts
    333
    Quote Originally Posted by dandyme View Post
    well?
    Don't you just hate it when that happens?

  7. #7
    Join Date
    Feb 2011
    Location
    Fogelsville, Pa.
    Posts
    114
    Sorry guys I usually get back, I've been busy. To close the post, I replaced the board and the sensor. It wasn't going in to defrost, bad board. Thx for your input.

  8. #8
    Join Date
    Feb 2012
    Location
    tenn
    Posts
    3
    JUMP RED TO DFT TOUCH PINS TOGETHER A FEW TIMES SHOULD START DEFROST IF NOT CHANGE BOARD

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