What causes sudden engine stall when idling with AC on?
2 Answers
Sudden engine stall when idling with AC on occurs because the clutch is released too quickly. Reasons: The air conditioning refrigeration system is a major energy consumer for the engine. When the refrigeration system is activated, 10% to 15% of the engine's power is required to drive the refrigeration compressor and fan. If such significant resistance is suddenly added during engine idling, it is highly likely to cause the engine to stall due to insufficient power. Solutions: When the A/C switch is pressed for cooling, there is usually a request signal sent to the engine control unit first. After considering all relevant conditions and granting permission, the engine control unit will first increase the engine speed through the throttle control system before engaging the compressor, thereby avoiding stalling caused by the sudden additional load.
I encountered the same situation last time - the engine suddenly stalled while idling with the AC on. After inspection, I found the main cause was excessive carbon buildup in the engine, particularly around the throttle body. The carbon deposits affected air intake, making the engine work harder. When the AC compressor kicked in, the additional load became too much to handle. Another issue was insufficient fuel pump pressure - inadequate fuel supply led to an overly lean air-fuel mixture, making stalling more likely. A stuck idle control valve or faulty mass airflow sensor could also prevent the ECU from properly adjusting idle speed. Alternatively, it might be due to a failing alternator or battery causing significant voltage fluctuations that disrupt the ignition system when the AC is on. Next time this happens, I recommend first cleaning the throttle body, checking fuel pressure and sensors, and testing battery voltage if necessary. For regular maintenance, periodic carbon cleaning can help prevent this issue.
