P0645 — A/C Clutch Relay Control Circuit

P0645: A/C Clutch Relay Control Circuit — what it means, the affected system and what to check before replacing parts.

Meaning, symptoms, causes and checks

A/C Clutch Relay Control Circuit. Basic catalogue definition; diagnostic details have not yet been reviewed.

Affected system: Powertrain

Symptoms

  • Air conditioning may no longer cool the cabin.
  • On systems with a compressor clutch, clutch engagement may fail.

Possible causes

  • The A/C clutch relay or its fuse may be faulty.
  • Wiring or connectors in the control circuit may be damaged or corroded.
  • An electrical clutch fault or controller issue is possible.

What to check

  • Confirm the vehicle uses the described compressor-clutch circuit.
  • Inspect the A/C fuse, relay and electrical connections.
  • Check the relay control signal against the vehicle's circuit diagram before replacing components.

Also written as: P0645-00, P064500, PO645 (some scan tools add the fault-type byte, e.g. -00).