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    lp1964's Avatar
    lp1964 Posts: 3, Reputation: 1
    New Member
    		  
    #1

    Oct 30, 2008, 03:52 PM
    Lennox Furnace fan only runs on slow speed in heating mode
    I hope someone out there can help me under the control logic and components on my 1994 Lennox G20RE gas furnace.
    My fan runs at normal speed when it runs alone.
    When the furnace is in the "heat" mode, the fan only runs at minimum speed.
    It then overheats and begins to smell like it's burning up. Hot air comes out of the ducts at a minimal airflow rate, especially the overhead return? Ducts.
    What component on the BCC2 panel controls that circuit?
    Thanks for any help you can offer!
    Laurie
    mygirlsdad77's Avatar
    mygirlsdad77 Posts: 5,713, Reputation: 339
    Plumbing Expert
    		  
    #2

    Oct 30, 2008, 04:04 PM

    Follow the wires from your blower motor to the control board. They should read something like this... heat, cool, fan, spare. Now look at your wiring diagram located inside one of the covers of your furnace. It should tell what colors correspond to speeds. Put a higher speed wire on the heat terminal on the board. Let me know what you find, and I will try to help further.

    That said, your furnace should work just fine with the factory wiring. Sounds like you may have other factors causing your problem. Check your filter. Do you have central ac? Let me know some details and I will help as best I can.
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert
    		  
    #3

    Oct 30, 2008, 04:18 PM
    Usually furnaces are designed to run on slow speed in the heat mode.
    How long has this been a problem? The reason I ask is that it was set from the factory to be on low speed and it has been running that way since 1994, What has changed? Did someone close off registers? Block the return air supply?
    lp1964's Avatar
    lp1964 Posts: 3, Reputation: 1
    New Member
    		  
    #4

    Oct 30, 2008, 04:28 PM

    When we put the higher speed wire on the heat terminal on the board the fan ran at the correct (normal) speed.
    The filters are actually out of the furnace right now as that was my first thought too... plugged ducting - that doesn't appear to be the problem.
    I don't have central AC.
    It seems like there must be a relay that kicks the fan into a higher speed once the furnace heats up - but it is not currently completing that circuit under those conditions. I'm not exactly sure how the control logic works so I am just guessing here...
    Is there a temperature sensor somewhere that might be going bad?
    Thanks so much for your help!
    Laurie
    lp1964's Avatar
    lp1964 Posts: 3, Reputation: 1
    New Member
    		  
    #5

    Oct 30, 2008, 04:45 PM

    The ducts are not blocked and no - nothing has changed. I did have the BCC-2 board (or just a component of that control board) replaced a couple years ago, and the service tech didn't have the part on hand, so he jumpered something - not sure what - to make the furnace run until the part came in. That is about all that has been touched on this unit up to this point.
    Thanks for your input!
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