Unjump an HVAC fan

Discussion in 'HVAC Heating & Cooling' started by spfrancis, Jul 13, 2020.

  1. spfrancis

    spfrancis Member

    Joined:
    May 31, 2014
    Location:
    Virginia
    So I had a problem in the middle of July 4th weekend, and I had to call the HVAC guy to get my HVAC running with a house full of folks. He said that he had to replace a transformer, and that my control board was not sending the signal for the fan to come on. He replaced the transformer, and then he jumped the fan so that he could have the fan run 24/7. It has been working.
    I know that I need a new control board. My control board is a honeywell 9160 control board. I went to supplyhouse and bought a universal honeywell 9120 board. Here is a picture of my current board:
    I can see that the cool tab is not on there any more. My thought is that he wired the cool jumper to some constant power source to get the fan to come on. I was trying to see what are the ways to get constant power to the cool wire going to the fan(hi) to make it stay on?
    Any help would be appreciated.
    I have mapped out all the other wires for the board swap based on what came with the universal board.
     

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  2. fitter30

    fitter30 Active Member

    Joined:
    Feb 2, 2020
    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    Oem boards even though they have the first numbers the second set of numbers that you have found are different.
    your UL rating with that new board is gone. What are the compleate numbers of both boards and model /brand of furnace. Does your heat work?
     
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  4. WorthFlorida

    WorthFlorida The wife is still training me.

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    The green wire from the thermostat to the air handler control board brings power to the fan motor relay. The red wire between the two is 24v ac. either at the transformer or thermostat wire he jumped the red to the green. OEM universal control board will work if all you have is a basic system. If you have a schematic for the control board it isn't that hard to make the change. Thw wire to from the thermostat is the same, the leads for the compressor and blower motor in the air handler may take a little doing. There should be a 24v and a Common for the transformer leads.

    Is this a forced air furnace with a AC coil on top of it. If yes the control board wiring gets a little involved to make a match.
     
    Last edited: Jul 15, 2020
  5. spfrancis

    spfrancis Member

    Joined:
    May 31, 2014
    Location:
    Virginia
    Sorry I didn't see this until last night. So I did the cutover, and the AC, and fan seemed to be okay. I was able to map all the wires from the documentation that was provided for the universal 9120 -> 9160 unit. I was just a little nervous about the "unjumping". I could see that the "cool" tab off off, so the question was where the guy jumped it too. I saw one 3 wire wrapped wingnut, that had the black wire from the fan, then going to "L1" and the black wire off of the transformer. I just pulled the fan wire off, and it seems to be working fine, and the fan is now coming off and on.
    I will wait for the fall/winter to try turning on the furnace, and make sure that the heater is working correctly. This saved me a bundle.
    From $500 down to $110.
    THanks for the help.
     
  6. WorthFlorida

    WorthFlorida The wife is still training me.

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    FYI... In heat mode the fan start is delayed (for gas or fuel oil) to give the furnace time to heat up the plenum, with electric heat the fan starts immediately. In cool mode the fan immediately turns on when calling for cooling. Depending on the unit and thermostat, there is a delay in turning off the fan motor to just get a little more heating or cooling energy out of the run cycle.
     
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