Description
The Johnson Controls T-4002-302 is a reverse acting pneumatic thermostat kit specifically for use in two-pipe HVAC systems, where the existing thermostats are single-temperature models. The mechanism of its operation is based on the pressure of air in order to control the temperature in a room. When the room temperature rises, the thermostat contracts and decreases pressure in a control line. This opens a pneumatic valve to shut off the hot water or steam supply to the heating unit. On the other hand, when the room temperature is low, the thermostat expands, the pressure rises and the valve opens the supply.
