The "Y" terminal on the thermostat is used for which component?

The "Y" terminal on a thermostat is specifically designated for the cooling function, which activates the cooling contactor coil. When the thermostat detects that the indoor temperature has exceeded the desired setpoint, it completes the circuit to the "Y" terminal. This action sends a signal to the cooling system to engage the compressor and often the outside condensing unit, thereby initiating the refrigeration cycle.

This connection is crucial as it allows the thermostat to control when cooling is needed, ensuring efficient operation of the air conditioning system. The other components listed, such as the heating contactor coil, blower relay coil, and defrost heater, have their distinctive terminals and functions, which do not relate to the cooling process managed by the "Y" terminal. Understanding this distinction is essential for troubleshooting and maintaining HVAC systems effectively.