Digital thermostat mounted on a concrete wall
Generic photo: Alexander Mass · Pexels License

Installing a C-wire adapter (Nest Power Connector, ecobee PEK and similar)

An adapter mounts at the furnace/air-handler board and lets the existing wires carry both the calls and constant 24 V. Check compatibility first: dual-transformer, fan-coil and communicating systems are commonly excluded.

Cross-checked ~45 min moderateBrands: Google Nest, ecobee, Others

Before you start

  • Power off at the furnace switch/breaker before opening the cabinet
  • Connect only to the 24 V terminal strip

Diagnostic steps

Unlock all 5 steps with expected values

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OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

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