Posted on 7/31/2026
Turning on the air conditioning adds work to the engine. The A/C compressor has to be driven by the belt, and the cooling fans may begin operating at the same time. A healthy engine usually compensates by adjusting idle speed and fuel delivery, so the change should be minor. When the engine begins shaking, stumbling, or nearly stalling with the A/C on, the added load is exposing a weakness. The cause may be related to the compressor, belt drive, engine mounts, throttle body, ignition system, or the controls responsible for maintaining idle. The A/C Compressor Adds Load To The Engine The compressor circulates refrigerant through the air conditioning system. When its clutch engages, or its internal control changes output, the engine has to supply additional power. At idle, that added demand is easier to feel because the engine is already turning slowly. A brief change in engine tone can be normal. Repeated shaking, a large RPM drop, or a feeling that the engine may s ... read more