When you are installing a 24V thermostat, to which terminals of the thermostat should you connect the 24VAC power supply and what color wires would you use?

When you are installing a 24V thermostat, to which terminals of the thermostat should you connect the 24VAC power supply and what color wires would you use?

• A. C terminal, blue or black
• B. R terminal, red
• C. G terminal, green
• D. Y terminal, yellow

Answer: (A)

A 24V thermostat needs a complete circuit from the transformer, so power is delivered across the R and C terminals. The common side of that supply is wired to the C terminal, and the color convention for that leg is blue or black. The other leg of the 24VAC supply goes to the R terminal, typically with a red wire. This setup powers the thermostat’s electronics; the G and Y terminals are for separate control signals (fan and compressor) and are not used to carry the power.

A 24V thermostat needs a complete circuit from the transformer, so power is delivered across the R and C terminals. The common side of that supply is wired to the C terminal, and the color convention for that leg is blue or black. The other leg of the 24VAC supply goes to the R terminal, typically with a red wire. This setup powers the thermostat’s electronics; the G and Y terminals are for separate control signals (fan and compressor) and are not used to carry the power.