Can the car air conditioner be turned on with only the power on?

[MacMia]

Car air conditioner can be turned on with only the power on. Here is the relevant introduction of car air conditioner: Compression: The compressor inhales the low-temperature and low-pressure refrigerant gas at the outlet of the evaporator and compresses it into high-temperature and high-pressure gas to discharge the compressor. Heat dissipation: The high-temperature and high-pressure superheated refrigerant gas enters the condenser. Due to the decrease in pressure and temperature, the refrigerant gas condenses into liquid and discharges a large amount of heat. Throttling: The refrigerant liquid with higher temperature and pressure passes through the expansion device, its volume increases, and the pressure and temperature drop sharply, discharging the expansion device in the form of mist (fine droplets). Heat absorption: The mist-like refrigerant liquid enters the evaporator. Since the boiling point of the refrigerant is much lower than the temperature in the evaporator, the refrigerant liquid evaporates into gas. During the evaporation process, it absorbs a large amount of surrounding heat, and then the low-temperature and low-pressure refrigerant vapor enters the compressor again.

[AbelLynn]

When the car is powered on but the engine isn't started, the air conditioning button may light up, but honestly, you won't get actual cold air. The reason is that the cooling function of the air conditioning system relies on the engine's operation to power its core components—it's essentially a power-dependent device. In this state, the AC fan can blow air, but it's just natural air or residual warm air; don't expect any cooling effect. I've tried this a few times in my home garage—pressing the button while waiting for someone, hoping for some cool air. The result was strong airflow with no chill, and it drained the battery so much that the car almost had trouble starting, affecting normal vehicle operation. My advice: don't rely on this state for cooling. It's only suitable for short-term ventilation, especially during scorching summer days when the car interior feels unbearable. A bit of airflow is better than nothing, but to preserve battery life, it's best to quickly start the engine or leave the car with windows open—saving money and ensuring safety.

[VanBella]

In my daily car usage, I tried turning on the AC with only the ignition on—the button light was on, and the fan was whirring, but the air wasn't cold at all. I learned that the core cooling function of the AC relies on the engine running to activate the power chain. In this state, it's only half an AC: the fan can blow some air, at best like a small fan circulating air inside the car, not suitable for staying long. I recalled one time when I picked up my child from school, I turned on the AC in advance to cool down, but the fan just blew loudly without cooling, and the battery drained quickly. This got me thinking: if waiting in the car for no more than 10 minutes, ventilation is fine, but don’t expect cooling; for real comfort, it's better to have the engine running or find a shady spot to rest.

[Stewart]

When the car is only powered on and the air conditioning is turned on, the fan will work and blow air, but there's no way to get cold air. This is mainly because the cooling system requires the engine to be running to drive it, so it's essentially just using the ventilation function. Over the years of driving, I've tried it a few times—waiting in the car with the air conditioning on without starting the engine. The airflow is strong, but it's just natural air. Prolonged use can drain the battery significantly, potentially causing difficulty when starting the car later and affecting the next drive. It's advisable not to expect cooling in this mode, but short-term ventilation is feasible, such as when smoking in the car or clearing odors—a few minutes won't cause issues. On hot days, opening the windows for additional airflow is even better.