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TB7980 2-10 vdc modulating thermostat


The TB7980 thermostat is specified as a 2-10vdc proportional output thermostat.  We have an issue whereby the thermostat will not output anything more than 9.3 volts maximum.  It will not fully close our normally open 2-10vdc actuator (2=open / 10=closed).  In an email response to our concern, the manufacturer claims the 10vdc is a nominal output and by design it will not produce the full 10 volt output.

I am asking the help of anyone who has this thermostat installed to take a DC voltage reading at the actuator.  You would read the terminal outputs 3+ and 4 common.  If terminal 4 is not being used, you would read 3+ and 2 common. 

The reading would be taken by manipulating the setpoint higher in heating or lower in cooling while the “full black bars” are displayed on the output power LCD display.  You may need to remove the thermostat from the subbase to confirm it is a TB7980 and not a TB6980.  If it is a TB7 please also note the 4 digit date code in your response.

This Honeywell thermostat is ID’d as 4” x 2” vertically mounted euro white in color with an LCD display and 3 pushbuttons being an up and down arrow and an override.  It is often used on VAV systems.  Thank you.


  • PeterNH
    PeterNH Member Posts: 88

    If you have a Radio Shack breadboard learning experiment station....

    It would be possible to use a 741 op amp and work with the resitance values to add just enough voltage gain to get the output over 10 volts.

    Doable, if it is a critical need.

  • Wesman
    Wesman Member Posts: 16
    Work around

    Thanks for the input. 

    On Monday will  also look at changing out to Siemens or Peco stats.
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