Why does the car overheat when the AC is on?

[McBeckett]

The main reasons for engine temperature rise when using AC are as follows: 1. Cooling fan malfunction: Normally the electric cooling fan has two speeds - low speed and high speed. The high speed engages when AC system pressure is too high or when engine coolant reaches 103°C. 2. Insufficient thermostat opening: When the thermostat opening is too small at normal temperatures, it slows down engine coolant circulation, causing overheating at low speeds. 3. Water pump cavitation: If the water pump shaft cracks, it may cause cavitation when coolant temperature rises, leading to overheating. 4. Wiring issues: Poor grounding of the battery's negative cable or engine coolant temperature sensor may cause false high temperature readings on the gauge (known as false overheating).