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    zhuroy's Avatar
    zhuroy Posts: 6, Reputation: 1
    New Member
    		  
    #1

    Aug 22, 2009, 02:45 PM
    Lennox G24M 3/4-100A-7 blower not start if in cool
    The gas furnace: Lennox G24M 3/4-100A-7
    SN:6398B17474

    In T-start, If heat and cool off, fan in on position, furnace indoor blower will run; Also try heat with fan on, blower also run;

    however switch T-start to cool, regardless fan in on or auto, when outside condenser is started, the furnace blower will be immediately stopped.

    ACBCool-NEUTRALS(any pin) = 0 VAC
    Y-C = 24 VAC
    R-C =24 VAC

    It looks K3 relay in circuit board is dead.

    From the diagram, K3 also controls ACBHeat; In my case, when fan is on, heat mode, the blower is started. I don't test fan in auto when heat mode case my house is hot.

    Is it possible that my heat is also broken in auto fan mode?

    Can I change the K3 relay only in circuit board?

    Thanks
    hvac1000's Avatar
    hvac1000 Posts: 14,540, Reputation: 435
    Heating & Air Conditioning Expert
    		  
    #2

    Aug 22, 2009, 06:39 PM
    Usually the entire circuit board is replaced. I am not saying it cannot be done IF you can find a compatible relay but HVAC service persons just replace the board due to liability issues. I am sure there is a relay available that might work even if you have to use a remote add a relay type device and solder the wire extensions to the board. Been there done that but never on a customers equipment.
    zhuroy's Avatar
    zhuroy Posts: 6, Reputation: 1
    New Member
    		  
    #3

    Aug 23, 2009, 07:32 AM

    Thanks, sounds reasonable. I will see how I can proceed after my testing on heat/fan-auto is done.
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