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Refrigeration & Air Conditioning Mechanic Red Seal · Question

A technician is installing a new programmable thermostat. After wiring, the heating system runs constantly regardless of the setpoint. Which wiring error is most probable?

If the 'R' (24V transformer hot) wire is shorted to the 'W' (heat call) wire, the heating relay in the furnace or air handler will be continuously energized, ca

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Question: A technician is installing a new programmable thermostat. After wiring, the heating system runs constantly regardless of the setpoint. Which wiring error is most probable?

Answer options:

  • The 'C' (common) wire is disconnected.
  • The 'Y' (compressor) wire is shorted to 'G' (fan). ✅ The 'R' (24V transformer hot) wire is shorted to 'W' (heat call).
  • The 'O/B' (reversing valve) wire is not connected.

Correct answer: The 'R' (24V transformer hot) wire is shorted to 'W' (heat call).

Explanation: If the 'R' (24V transformer hot) wire is shorted to the 'W' (heat call) wire, the heating relay in the furnace or air handler will be continuously energized, causing the heating system to run without interruption.

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