complex thermostat requirement

Discussion in 'General Electronics Chat' started by bobrobert, Nov 14, 2013.

  1. bobrobert

    Thread Starter New Member

    Feb 9, 2013
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    I have a air conditioner to cool a building and a hot water system to heat it.
    Each have their own air mover (fan). They are being controlled by one conventional thermostat. The air conditioner it wired correctly except that the FAN wire isn't connected to the air conditioner air mover. FAN is connected to the hot water air mover. So..the heat has to be turned on and off manually. This is a very awkward situation. Anyone have any ideas on the best way to remedy this situation?
     
  2. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,039
    1,667
    Get a fancier more functional digital thermostat.

    There are many now that will do all that and more for less than $100.
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,028
    3,238
    Why can't you just connect the AC control signal to also control the AC fan and the heat control signal to also control the heat fan?
     
  4. #12

    Expert

    Nov 30, 2010
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    6,818
    This doesn't make sense: The fan command from the thermostat is wired to the heat system, making the heater fan fully automatic, therefore the heat has to be turned on and off manually.

    The air conditioner system is wired correctly except it isn't wired correctly so the fan doesn't come on.

    Want to try again?

    I think I have it. Wire the green fan command to the a/c air handler and use the white command wire to turn on the fan relay in the heater.
     
    Last edited: Nov 14, 2013
  5. inwo

    Well-Known Member

    Nov 7, 2013
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    315

    That's the way to do it.

    Or vice versa, use the yellow to pull in fan relay on cooling.

    Leave which ever system connected to green that you want manual fan control.

    What makes this system odd is that most heating systems use a type of thermodisc heat sensor to turn fan on. This prevents blowing cold air and keeps fan on until residual heat is removed.
     
  6. #12

    Expert

    Nov 30, 2010
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    6,818
    yes. I'm thinking, where's the stack switch (or similar)? The heater should be controlling its own fan.
     
  7. crutschow

    Expert

    Mar 14, 2008
    13,028
    3,238
    If it uses hot water for heating then perhaps the radiator is hot all the time and only the fan is turned on and off to control the temperature. In that case there wouldn't be a thermodisc switch to control the fan.
     
  8. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
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    In that case conventional wiring.


    W to heat air mover
    G to AC fan control
    Y to AC contactor

    Red from both transformers
    Yes you can! As long as nothings grounded.
     
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