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    dubya's Avatar
    dubya Posts: 1, Reputation: 1
    New Member

    Sep 23, 2005, 09:37 PM
    Furnace Blower Fan Won't Turn Off
    Last night I installed a brand new programmable Honeywell to replace my the ancient mercury Honeywell that was on the wall. I have a 20+ year old forced air gas with central air.

    The side effect has been that the furnace blower will not shut off. Whether the system is in "heat" or "cool" or "off" and the fan in "auto" or "on", the blower will not stop running.

    The wiring was fairly simple from the first four lettered terminals was as follows: G (Green Colour), Y (Yellow Colour), W(White Colour), R (Blue Colour) all matched up between both thermostats. However, on the old Honeywell, the 5th wire (Red Colour) was labelled "A". I took this to mean Rc. I put it in the Rc position and now the fan is on all the time.

    Any suggestions??

    I would appreciate some help on this.

    Please help me, it is getting cool very quick here in Ontario.


    labman's Avatar
    labman Posts: 10,580, Reputation: 551
    Uber Member

    Sep 24, 2005, 06:58 AM
    As background, usually there is a 24 volt AC transformer in the furnace with the secondary winding connected to a red wire running to the thermostat and a blue wire, common, to the gas valve, A/C relay, and fan relay. From the thermostat there will be white wire to the gas valve, yellow to the A/C, and green to the fan. The thermostat is wired to switch the power from the red to the white, yellow, and green as needed with the blue completing the circuit. Most thermostats and furnaces have the contacts labeled R, B or C, W, Y, and G for the corresponding wire colors. It may be wired to have the A/C control wires return to the furnace and its controls and then a second wire goes to the A/C unit. Internal wiring may replace the green wire if the thermostat does not give you the option of fan only or continuous fan. Digital or programmable thermostats may need the blue wire connected to them.

    Start by removing the red wire. If that doesn't shut the fan off, you have a confusing case of something else going wrong when you worked on the thermostat. Could be disturbing the wires shorted the red and green. If it does, somehow the thermostat is switching the Rc wire to the G terminal. Carefully read the manual, and make sure there isn't some default program etc. that turns on the fan. Check to see if you have 24 volts between the green and blue. If so, and you are absolutely sure the thermostat has the fan switched off, and it still runs, take the thermostat back and complain.
    restez's Avatar
    restez Posts: 3, Reputation: 1
    New Member

    Jan 9, 2011, 09:08 PM
    You have a limit switch gone bad check switches with power on it should read like .023... a closed switch
    If it reads 24v its bad. When they go bad the blower stays on as a safety device telling you there is a problem
    funrich5109's Avatar
    funrich5109 Posts: 1, Reputation: 1
    New Member

    Sep 18, 2012, 11:51 AM
    Some one gave me old blower fan out of furance has four wires I just want to make a box fan out of it it has four wires what color wires do I use to hook to 110 volts to socket on the wall which is 110 volts thanks for any help

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