Yes, when you turn off the engine of a car, the air conditioner (AC) will stop blowing cold air. The reason for this is that the car's air conditioning system relies on the engine's power to operate. The engine drives the compressor, which is a critical component of the AC system responsible for circulating the refrigerant and cooling the air.
When the engine is running, the compressor is activated, and it compresses the refrigerant gas, raising its pressure and temperature. As the hot, pressurized refrigerant passes through the condenser coil located at the front of the vehicle, it releases heat to the surrounding air and condenses into a high-pressure liquid.
The liquid refrigerant then travels through the expansion valve or orifice tube, where it undergoes a rapid pressure drop, turning it into a low-pressure, cold mist. This cold refrigerant flows through the evaporator coil inside the car's cabin. The warm air from the interior passes over the evaporator coil, and as a result, the refrigerant absorbs the heat from the air, cooling it down. The cooled air is then blown into the cabin by the blower fan, providing the desired cooling effect.
However, when you turn off the engine, the compressor stops working, and the refrigerant stops circulating through the system. As a result, the AC system is no longer able to cool the air, and the air blowing into the cabin will gradually return to the ambient temperature outside the vehicle.
It's important to note that some modern cars have auxiliary systems that can provide limited cooling even when the engine is off, using stored energy from the car's battery. These systems are typically designed to provide temporary relief while parked, but they may not be as effective or long-lasting as when the engine is running and the main AC system is active.