The thermostat terminal normally assigned to cooling control is which?

• A. G
• B. W
• C. R
• D. Y

Answer: (D)

Cooling is controlled through the Y terminal. When the thermostat calls for cooling, it connects the 24-volt supply from R to Y, energizing the cooling circuit and turning on the compressor/indoor-outdoor condenser pair. The other functions are handled by the remaining terminals: W for heat, G for the fan, and R is the 24V power source. On most systems you’ll see a yellow wire to Y, which is a helpful cue that this path triggers cooling. In heat pump setups, Y still drives the compressor, though other controls may be involved for mode changes.