A car's air conditioner may not work effectively or may not work at all when the car is parked due to the following reasons:
Engine-driven system: In most cars, the air conditioner is powered by the engine. When the engine is not running, such as when the car is parked and turned off, there is no power source to operate the air conditioning compressor. As a result, the AC system won't work.
Low refrigerant pressure: The air conditioning system requires a specific amount of refrigerant (usually a gas or liquid) to operate effectively. When the car is parked and the engine is off, the refrigerant pressure in the system equalizes, and some refrigerant may return to the compressor, causing a temporary decrease in pressure. This can lead to reduced cooling performance when you restart the car and turn on the AC.
Battery drain concerns: If the car's air conditioner were to operate while the engine is off, it would draw power from the car's battery. Using the AC for an extended period while the engine is off could drain the battery, making it difficult to start the car later.
Safety reasons: To prevent potential accidents or mishaps, some vehicles are designed not to allow the air conditioner to operate when the engine is off. This prevents drivers from accidentally leaving the AC on, which could lead to battery drain and other issues.
To get the best performance from your car's air conditioner, it's generally recommended to run the engine while using the AC. However, if you want to keep the car cool while parked without running the engine, you can consider using auxiliary devices like window shades or sunshades to block direct sunlight, which can help reduce the interior temperature of the car.
Keep in mind that if you notice persistent issues with your car's air conditioner, such as poor cooling or strange noises, it's essential to have it inspected and serviced by a qualified mechanic or an automotive air conditioning specialist. They can diagnose and resolve any problems, ensuring your AC operates optimally when you need it.