A car's air conditioner does not work or provides limited cooling when the car is parked because the AC system relies on the engine running to operate properly. The air conditioning system in a car is driven by a belt connected to the engine's crankshaft, and it requires the engine to be running to function effectively. When the engine is not running, the AC compressor, which is responsible for compressing and circulating the refrigerant, does not receive power, and therefore, the cooling process does not take place.
Here's why the AC doesn't work when the car is parked and the engine is off:
Power Source: The AC compressor, as mentioned earlier, is driven by a belt that connects to the engine. The engine's rotation powers the compressor, allowing it to compress the refrigerant gas and cool the air. When the engine is off, there is no power source to drive the compressor.
Electrical Load: Running the air conditioner requires a considerable amount of electrical power to operate the compressor, fans, and other components. If the AC were to run while the engine is off, it could quickly drain the car's battery, leaving it unable to start later.
Engine Cooling: The AC system also works in conjunction with the engine's cooling system. The AC condenser, which is responsible for dissipating heat from the refrigerant, is located in front of the engine's radiator. When the car is moving, the air flowing through the condenser helps cool the refrigerant and prevents the AC system from getting overwhelmed. When the car is parked, there is minimal airflow, which can result in reduced AC performance.
To summarize, a car's air conditioner requires the engine to be running to operate efficiently and safely. It is designed this way to prevent unnecessary battery drain and to ensure that the AC system works optimally in conjunction with the engine's cooling system. If you want to use the air conditioner while parked without the engine running, some vehicles offer a "auxiliary" or "accessory" mode, which allows you to use certain electrical systems, including the AC, for a limited time while preserving enough power to start the engine afterward. However, prolonged use in this mode can still significantly drain the car's battery, so it's essential to use it judiciously and be mindful of the battery's state of charge.