* Low Battery: The AC compressor requires a significant amount of power to operate. A weak or low battery might not be able to provide enough current to both run the engine and the compressor simultaneously, leading to a stall.
* Alternator Issues: The alternator is responsible for recharging the battery while the engine is running. A failing alternator won't generate enough power to keep up with the demands of the AC compressor and the car's other electrical components, resulting in a stalled engine.
* Loose or Corroded Battery Cables: Poor connections between the battery and the rest of the electrical system can lead to insufficient power delivery, causing stalling when the AC is turned on (a higher power draw is more likely to expose a weak connection).
* Failing AC Compressor: While less common, a seizing or heavily worn AC compressor can put an exceptionally high load on the engine, causing it to stall, especially if the engine is already running poorly or is low on power. (This usually results in a noticeable loud grinding noise from the compressor as well).
* Idler Pulley Problems: The idler pulley supports the serpentine belt which drives the AC compressor. A seized or failing idler pulley will put extra strain on the engine, potentially leading to a stall when the AC is engaged, especially in older vehicles with higher mileage.
* Engine Problems: In some cases, an underlying engine issue (like low compression, dirty fuel injectors, or a failing ignition system) can make the engine less able to handle additional load, causing a stall when the AC is turned on. This indicates a more serious problem beyond just the AC system.
* Low Engine RPM: If your engine is already idling too low, adding the load of the AC compressor can push it below the minimum RPM required to keep it running.
To diagnose the problem, it's best to take your car to a qualified mechanic. They can perform tests to identify the specific cause and recommend the appropriate repairs. Simply checking the battery voltage and alternator output is a good first step, but a comprehensive inspection is generally needed for a definitive diagnosis.
