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R to g

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johnjohn89
johnjohn89 Member Posts: 100
edited July 2023 in A-C, Heat Pumps & Refrigeration

Guys what should u reading voltage between r to g during the heating mode? 28v or ov? Some unit I work on when during the heating mode I do get voltage readings between r and g, other I don’t , but I do believe that g get power by other , doesn’t power same time 

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  • ratio
    ratio Member Posts: 3,641
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    Depends on how the control board is built. Some may back feed the G terminal when the limit turns the fan on, some may not.
    johnjohn89
  • pecmsg
    pecmsg Member Posts: 4,871
    edited July 2023
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    If a switch is closed you get 0 voltage
    if a switch is open you get voltage
    STEVEusaPASuperTech
  • HVACNUT
    HVACNUT Member Posts: 5,844
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    There's so many different ways to wire the fan for heat mode. Some will use G, and some won't. 
    A PSC motor could get direct line volt power from an aquastat, or an internal time delay relay.
    A variable speed could get voltage on W1 and start the fan. Voltage at W2 will increase fan speed. 

    The wiring you see where G is powered for fan in heat mode is usually done at the thermostat. There will be a "gas/electric" switch, or it will ask during installer setup "equipment or thermostat controls fan in heat mode".
    johnjohn89
  • johnjohn89
    johnjohn89 Member Posts: 100
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    ratio said:
    Depends on how the control board is built. Some may back feed the G terminal when the limit turns the fan on, some may not.
    That’s what I looking for thanks
    pecmsg said:
    If a switch is closed you get 0 voltage
    if a switch is open you get voltage

    depends on what energized the blower, some unit r and g not energized by thermostat, 
  • johnjohn89
    johnjohn89 Member Posts: 100
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    HVACNUT said:
    There's so many different ways to wire the fan for heat mode. Some will use G, and some won't. 
    A PSC motor could get direct line volt power from an aquastat, or an internal time delay relay.
    A variable speed could get voltage on W1 and start the fan. Voltage at W2 will increase fan speed. 

    The wiring you see where G is powered for fan in heat mode is usually done at the thermostat. There will be a "gas/electric" switch, or it will ask during installer setup "equipment or thermostat controls fan in heat mode".
    That’s what I looking for , u the man

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