Central Air Conditioner and Refrigeration explains that air conditioning thermostats work by relying on air current. They either have bimetals or a thermistor that sense the air current returning to the return ducts.
Central Air Conditioner and Refrigeration states that an AC thermostat determines the room temperature through the random air current that passes through it. Then, it compares the room temperature with the setpoint temperature.
ACME DIY explains that a thermostat regulates the operation of the heating and cooling equipment in households. When a thermostat is set to a specific temperature, it turns the equipment on or off to maintain the desired temperature.
ACME DIY lists two basic kinds of thermostats: electromechanical and electronic. An electromechanical thermostat uses a bimetal coil that contracts or expands whenever temperature changes. A glass vial containing mercury is attached to the bimetal strip. When the vial tilts on the back of the strip, the mercury flows to the vial’s end where there are two exposed electrical contacts. A low voltage circuit is created as the mercury envelopes these electrical contacts. This works like a light switch, allowing a circuit to turn on the AC or heater. An electronic thermostat uses a sensor to detect varying levels of temperature. The thermostat electronically allows a circuit to turn the AC or heater on when the detected temperature differs from the specified temperature.