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  1. #1
    Join Date
    Nov 2013
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    Confused thermostat issue

    I am an electrician by trade.

    I have a tempstar ntc6075fbai furnace. I want to put in a new thermostat. The voltage at the thermostat is 30v, instead of 24. What could be causing that. ?

    (The transformer on the controller board is 24v and it reads 24 volts on the output)

  2. #2
    Join Date
    Aug 2007
    Location
    Winter Haven, FL
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    On the board, if you measure across the "R" and the "C" terminals, you should get the same voltage at the wall thermostat. If you measure on the board, you might be on a regulated power supply line for the logic circuits. Secondary voltage should be input voltage divided by 4
    120v/4= 30v
    115v/4 = 28.75v
    110v/4 = 27.5

  3. #3
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
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    Quote Originally Posted by Joe Harper View Post
    On the board, if you measure across the "R" and the "C" terminals, you should get the same voltage at the wall thermostat. If you measure on the board, you might be on a regulated power supply line for the logic circuits. Secondary voltage should be input voltage divided by 4
    120v/4= 30v
    115v/4 = 28.75v
    110v/4 = 27.5
    Makes sense and is the same thing I've seen in the field. Not sure how he's only getting 24v @ the transformer but 30v @ the thermostat.

    Martuuuu, are you reading directly across the transformer terminals or from one side to ground/other point?

  4. #4
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    Nov 2013
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    Quote Originally Posted by 54regcab View Post
    Makes sense and is the same thing I've seen in the field. Not sure how he's only getting 24v @ the transformer but 30v @ the thermostat.

    Martuuuu, are you reading directly across the transformer terminals or from one side to ground/other point?
    Directly across the transformer terminals reads 24.

  5. #5
    Join Date
    Aug 2007
    Location
    Winter Haven, FL
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    Are the thermostat wires and the 120v wires run together?

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