P0645: Air Conditioning Clutch Relay Control Circuit
What to do
Driveable, with air conditioning that does nothing. The refrigerant system itself is probably fine — this is the electrical command to engage the compressor, so be cautious about a regas being suggested before the circuit is checked.
What this code means
A fault in the circuit controlling the air conditioning compressor clutch relay. The engine module switches the compressor rather than the climate controls doing it directly, so that it can raise idle first and cut the compressor during hard acceleration or if the engine is running hot.
A fault here means the compressor is never engaged, so the air conditioning blows ambient air. The system is otherwise intact, which is worth knowing before a regas or a compressor is proposed.
Likely causes
Start here
- Failed air conditioning clutch relay · easy
- Corroded or loose connector · easy
- Broken wire in control circuit · moderate
Less common
- Failed compressor clutch coil · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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