Which thermostat terminal is used to signal the compressor to start?

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Multiple Choice

Which thermostat terminal is used to signal the compressor to start?

The signal to start the compressor comes from the cooling call. When the thermostat wants cooling, it closes the circuit from the 24V supply (R) to the cooling terminal (Y). This sends 24V to the outdoor unit’s contactor coil, energizing it and turning on the compressor (and the condenser fan). The other terminals have different roles: W is for heating, G controls the indoor blower, and R is simply the power feed. So the Y terminal is the one that signals the compressor to start.

The signal to start the compressor comes from the cooling call. When the thermostat wants cooling, it closes the circuit from the 24V supply (R) to the cooling terminal (Y). This sends 24V to the outdoor unit’s contactor coil, energizing it and turning on the compressor (and the condenser fan). The other terminals have different roles: W is for heating, G controls the indoor blower, and R is simply the power feed. So the Y terminal is the one that signals the compressor to start.

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