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Problem: My Heat Pump Defrost Control Board is Bad. Can I Bypass the Defrost Control Board to Get Cooling?

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Problem: My heat pump defrost control board is bad. I can not use my heat pump because the defrost control board is bad. We are burning up in our home without air conditioning. Techs are days behind before they can come and fix our problem. It will be days before we receive a new defrost board replacement because of shipping time. Is there any way that I can bypass the defrost control board so we can get the air conditioning to cool our home?  Please help if you can!

Answer:  Yes! I can help! We have this question asked quite often so I decided to write a post on how to temporarily bypass a heat pump defrost control board so people can get their air conditioning working again. If you are good with your hands and know a little about electrical wiring then you should be able to bypass the heat pump defrost board. We have two really good YouTube videos that explain how to bypass a heat pump defrost board to allow for cooling or to allow for the air conditioning to work.  The first video was made by SuperCool Slide Rule. The second YouTube video was made by AC Service Tech LLC. Thanks to SuperCool Slide Rule and AC Service Tech LLC for making these great educational and informative videos!  I have the steps written down step by step below. If you need a new heat pump defrost control board then we sell many different name brand defrost control boards on the following page: Please click here if you are interested in the defrost control boards that we sell.  If you have any questions or would like for us to look up any parts then please email us anytime or comment below. Our email address is We Would Love to try and Help You Out and Earn Your Business! 

*Disclaimer: Arnold’s Service Company, Inc. assumes no liability for any incidental, consequential, or other liability from the use of this information. All risks and damages, incidental or otherwise, arising from the use or misuse of the information contained herein are entirely the responsibility of the user. Although careful precaution has been taken in the preparation of this website’s information, we assume no responsibility for omissions or errors.

Steps to bypass a heat pump defrost control board are:

  1. Turn off both high voltage and low voltage power by pulling the unit’s disconnect and turning the indoor air handler off. Test with a voltmeter set to “Volts AC” to make sure the power is off.
  2. I recommend taking a picture of how the defrost control board is wired before you make any changes to the board.
  3. For the heat pump to cool you will need to energize or have working three parts of the heat pump. (1) 220-volt condenser fan (2) the 24-volt contactor and the 24-volt reversing valve. Most heat pumps have the reversing valve energized in the cooling mode except Rheem and Ruud units. If you have a Rheem or Ruud unit then you would not need to do the part about energizing the reversing valve. 
  4. Identify the outdoor condensing fan relay and join the two fan relay wires together so that the outdoor condensing unit’s fan will run. Tape, insulate, and secure the two high voltage (210-245 volt) wires so that the wires do not touch or ground out to the body of your heat pump unit.
  5.  There are two low voltage wires that go to the 24-volt coil on the contactor. Disconnect, insulated, and secure the two existing wires from the contactor. I think it would be best to run two new wires to the 24-volt contactor coil.  One new wire on the power side of the contactor coil and one common “C” or ground wire on the opposite side of the power wire on the contactor.
  6. Join and wire nut together with the hot yellow (Y) wire that comes from the thermostat to one of the wires that go to the contactor (to energize the contactor) and the yellow (Y) wire should also be attached to the reversing valve orange wire. I would trace the low voltage wires down to make sure that you have the right wires that are going to both the contactor and reversing valve.  The contactor should have two wires (power and C) and the reversing valve should have two wires (power and C).
  7. FYI- To energize both the contactor and reversing valve the contactor has two low voltage wires that go to the contactor coil and the reversing valve should have two low voltage wires that go to the reversing valve coil. One of the two wires that go to both the contactor and reversing valve is the power wire which we will attach to the “Y” thermostat wire. The indoor thermostat when the thermostat calls for heat pump cooling takes the R (red wire from the 24-volt indoor transformer) and makes the connection to the “Y” wire to energize the contactor and make the contactor close. The other two wires from both the contactor coil and reversing valve coil is the C or called the common wire. For each device to be energized there must be a power wire “Y” and a C common wire attached.
  8. So we want to energize the fan, the contactor, and reversing valve in order to bypass the defrost control board. Next, you would want to connect the common wires together to the common side of the contactor and reversing valve. Join, and wire nut together with the other two contactor and reversing valve common wires.  Most of the time the blue thermostat wire is the common (C) wire. I would recommend that you take the cover off your thermostat and make sure and see which wire color is connected to the “C” “Com” connection on your thermostat. You would never want to directly connect the R and C terminals together because this would produce a direct short to ground and burn up many of the heat pump system’s low voltage controls if they are not protected by a low voltage fuse. 
  9. As a review: You should have two wires connected to the Y “Yellow” wire. One of the wires attached to the Y wire would go to one side of the contactor to provide power for the contactor and the other wire would go to the reversing valve to provide power for the reversing valve when your thermostat calls for cooling. The other common wire from your thermostat (you would need to make sure you have the right color for the wire that is attached to the C  “COM” of your thermostat). Two wires would be attached to this C common wire from your thermostat.  You would attach one of the wires to the C common side of the contactor and the other wire to the C common side of the reversing valve.  You should be ready to apply power and test. Best of luck. This should work if wired correctly.

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