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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.