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Problem: My furnace needs a new control board. Is there any way I can bypass the control board so I can run my air conditioner?

troubleshooting air conditioners and heat pumps

Problem: My furnace needs a new control board. Is there any way I can bypass the control board so I can run my air conditioning? We have this question asked quite often during the summer months. The problem is that the blower fan will not come on because the fan relay on the control board has failed. It is on the weekend when getting a control board is impossible or the person does not want to wait on a new control board to be shipped in before they can use their air conditioner.  It is hot and they need air conditioning now.  I wanted to make a post and write about how to bypass the control board to get air conditioning back on while waiting for a new control board.

Answer: This answer is intended to be used on PSC  (Permanent Split Capacitor) motors and not ECM (electronically commutated motors). If you have an ECM motor do not try this. If you have a 220-volt air handler do not try this.  If you are not comfortable working with electricity and working with your hands then do not try this. We here at Arnold’s Service Company, Inc. are not responsible for any injury or damaged equipment that might occur when doing this control board bypass. This answer is intended to help you get your air conditioning working again while you wait to have a new furnace control board installed. I feel so very sorry for people who have to wait on a control board to come in when wanting to run their air conditioner on those hot summer days and nights! I know that I would want to have air conditioning if there was any way possible! I hope this will help you get your air conditioner back on until you can get a new control board installed. We have a really good video below made by Travis Poe and HVAC contractor. Mr. Poe explains how he bypassed a furnace control board to run the blower by tying into the furnace door switch. This is an excellent idea! Thanks so very much to Travis Poe for making this great YouTube video. Below the video, I have another idea where I explain how to bypass the control board and connect the blower motor using an extension cord. You could use either method. Mr. Poe’s explanation seems to be a lot simpler than my explanation. 

You can also bypass the furnace control board with a heavy-duty extension cord as I describe here. This is the email I wrote to one of our potential customers when they asked if there was a way to bypass the furnace control board so the family could get air conditioning while waiting on a new control board. Here is my answer: The control board is used to start and stop the fan motor on your indoor furnace blower motor in both heating and air conditioning mode. There is a fan relay on the board that controls the blower motor. The control board should have nothing to do with the AC coming off and on because on most boards unless you have a high efficiency two speed AC. The only function of the control board for most AC installations is to provide a junction for the two Y wires at the furnace control board and the control board is not used to turn the outdoor unit off and on. The thermostat controls the AC outdoor unit to go off and on through the Y connection. The control board is used to turn the fan blower off and on. If you could by-pass your control board fan relay and run an extension cord to your fan blower motor then this would allow you to run your AC. You should be able to do this by turning the power off to your furnace and disconnecting the wires that go to your blower motor from the control board. Usually, there are 5 wires that come from the blower motor. Black, White, Blue, Yellow, and Red.  The Black, Blue, Yellow and Red wires are the furnace speed wires. The white wire is usually the neutral or common wire. You will only use two of the wires black and white coming from the blower motor to connect to the extension cord. I would suggest using a heavy gauge extension cord with at least 14 gauge wire because some blower motors require on the average 5 to 12 amps of power. You will need a good extension cord so it does not rob the blower motor of electricity. I would suggest using electrical tape to tape over the ends of the blower wires that you do not use so they will not short to ground.  You would hook the hot wire usually black (high speed)  on the blower to the black wire of a stripped extension cord with a wire nut then hook the white (neutral wire) of your blower motor to the white wire of the extension cord and plug the extension cord into a 120-volt outlet. The blower motor should start and run.  Turn your furnace back on so you will get 24 volts to the thermostat. Turn your thermostat to cooling and turn the thermostat down so your outdoor AC comes on. This should provide AC for your home. You will need to of course manually unplug the blower and turn up the AC thermostat when you want the AC to stop. I hope this helps you get air conditioning until your new control board arrives. God Bless you and your family today and always! Steve

 

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