Honeywell Pneumatic Calibration Instructions

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A pneumatic thermostat uses a control to adjust the ambient air temperature.
A pneumatic thermostat uses a control to adjust the ambient air temperature. (Image: Jupiterimages/Photos.com/Getty Images)

Thermostats are devices that are connected to the control system of a facility's heating and air cooling units. They are either dial- or digital-controlled and allow you to adjust the ambient air temperature inside the building. The thermostat uses sensors to measure the temperature and, based on the setting, sends information to turn on or off an air cooling or heating unit. Pneumatic thermostats, such as ones made by Honeywell, control the heating/air cooling system through a series of air-filled control tubes, which respond to pressure changes. Calibrating a Honeywell Pneumatic Thermostat requires the use of a pressure or psi gauge.

Turn the setpoint down slowly 5 degrees Fahrenheit below the actual room temperature on direct acting bimetal elements. Turn the setpoint up slowly 5 degrees F above the actual room temperature on direct acting bimetal elements. Check the thermostat to see if it bleeds off between 1 and 3 degrees F; if so, no further calibration is needed.

Remove the thermostat cover and attach a 30 psi gauge to the gauge tap.

Move the temperature setpoint indicator to the indicated temperature.

Turn the calibration screw until the gauge reads 0 psi for models TP970 and TP973. Move the "Day" calibration screw -- with 13 psi as the main air pressure -- until the gauge reads 0 psi for model TP971. Turn the "Summer" calibration screw -- with 13 psi as the main air pressure -- until the gauge reads 0 psi for model TP972.

Rotate the calibration screw in the opposite direction for all models until the gauge reads 8 psi -- plus or minus 1 psi; models TP970 and TP973 are now calibrated.

Move the "Nite" setpoint dial -- with 18 psi as the main air pressure -- until the setting agrees with the indicated temperature for model TP971. Rotate the "Winter" setpoint dial -- with 18 psi as the main air pressure -- until the setting agrees with the indicated temperature for model TP972; models TP971 and TP972 are now calibrated.

Remove the psi gauge and reattach the thermostat cover.

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