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    lostinspace1's Avatar
    lostinspace1 Posts: 2, Reputation: 1
    New Member
     
    #1

    Dec 31, 2008, 06:16 PM
    Switiching from Mercury to Digital Thermostat!
    I have a five wire system. I have a green, red, white, yellow, and blue. This is an electric heater attached to the air handler and a separate air conditioning system. THis system was controlled by a Lennox mercury thermostat. Could you tell me what each color wire does? Example: Yellow controls the outside unit. I am trying to switch this system to a programmable, digital thermostat.
    Have tried two Hunter programmable thermostats without success... the air conditioner and heater are running at the same time.
    I removed the yellow wire to cut off the air conditioner, the heat is working okay.
    Please advise.
    Stratmando's Avatar
    Stratmando Posts: 11,188, Reputation: 508
    Uber Member
     
    #2

    Dec 31, 2008, 06:25 PM

    I would go to Air Handler and see which each wire controls which contactor/relay, Red is likely hot(power), green can be fan, white is heat, I see yellow and blue for cool, 2 speed. All can be wrong and bad info. Verify all.
    dmrlook's Avatar
    dmrlook Posts: 134, Reputation: 8
    Junior Member
     
    #3

    Dec 31, 2008, 07:03 PM
    Are you sure the AC is running? Perhaps you have a heat pump and thus you see the compressor running outside and mistook that for the AC running. Generally speaking, any 5 wire controller will work with a fairly modern (within the last 15 years or so) system. And the previous post said what I would have said regarding the wire colors. You can always test to assure the red is the supply if you have a volt meter (should read 24 volts when connected to ground). Then, if you cross red and green, the fan should come on.

    Hope this helps.

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