User Guide

ManualsBrandsBarber Colman ManualsHVAC Replacement PartsDead Band Reverse Acting Thermostat

OPERATION

The deadband output (branch) pressure is factory set at

8 psig (55.2 kPa), placing both heating and cooling actuators

in the “off” (or closed) position. The output remains at that

pressure while the ambient (room) temperature varies within

the deadband. When the ambient temperature closely

approaches either the heating or cooling setpoint at either end

of the deadband, the output pressure changes at the rate of

approximately 3.3 psi/°F (41 kPa/°C). This modulates the

respective heating or cooling actuator from its closed position

toward its open position, while the other actuator remains in its

closed position. The temperature sensing assembly,

consisting of a deadband lever and two bimetal elements,

allows only one actuator at a time to be modulated toward the

open position.

CALIBRATION

Deadband Pressure Calibration

The deadband pressure is factory set at 8 psig. If necessary,

check calibration or adjust this pressure to meet application

requirements, as follows:

1. Remove the thermostat cover, using a 20-881 thermostat

wrench (1/4” hex wrench), and install a 22-138 branch tap

gauge adaptor and a suitable gauge into the branch

pressure tap hole (Figure-10 or Figure-11).

2. Be sure ambient temperature is between 65 and 75°F.

Turn the heating dial to 57°F and the cooling dial to 83°F.

3. Adjust the deadband pressure by turning calibrating

screw “A” (see Figure-10 or Figure-11), using a 20-881

thermostat wrench (1/16” hex wrench) until the desired

deadband pressure is obtained.

Setpoint Calibration

Direct-Acting Models

The direct-acting models are calibrated to have a 5.5 psig

branch pressure when the heating dial is set at ambient

temperature, and a 10.5 psig branch pressure when the

cooling dial is set at ambient temperature.

1. Refer to Figure-10. Using a 20-881 thermostat wrench

(1/16” hex wrench), gently turn screw “B” to position the

cooling dial to the 83°F setting. This moves the cooling

bimetal away from the deadband lever. Turn screw “C” to

obtain 5.5 psig output pressure. If there is a difference

between the ambient temperature and the dial reading,

rotate the dial gently to its stop and continue rotating screw

“C”, slipping the screw inside the dial. Rotate the dial back

to again obtain 5.5 psig. If the dial does not match the

ambient temperature, a second try may be required.

Figure-9 Direct-Acting Thermostat Operation.

Thermostat Output

Pressure Increase

Heating

Heating and

Cooling Off

Dead-Band

(adjustable)

Temperature Increase

Dead-Band Pressure

(factory set at 8 psig)

Dashed lines indicate reverse action.

Cooling

Direct Action