What are the effects of leaving the car air conditioning on overnight after the engine is turned off?
2 Answers
Leaving the car air conditioning system on after the engine is turned off can affect the vehicle's engine and battery. When the vehicle is started again, the air conditioning system will automatically turn on. This increases the load on the engine during startup, leading to an excessively high power load at the moment of ignition. Prolonged use in this manner can accelerate wear and tear on engine components, cause excessive carbon buildup in the engine, and severely deplete the battery, thereby reducing the vehicle's lifespan. After the engine is turned off, the air conditioning system relies on the battery's stored power. If the battery's stored power is completely drained, the battery will be depleted, making it impossible to start the vehicle. Car air conditioning cools by operating the air conditioning pump, which is powered by the rotation of the engine's crankshaft. When the engine is turned off, the crankshaft stops rotating, so the air conditioning pump ceases to function, and the air conditioning will not cool. Car air conditioning heats by transferring heat from the engine's coolant to the heater core inside the evaporator box, which is then blown out through the air conditioning ducts by the blower. When the engine is turned off, there is no heat to transfer to the heater core, so the air conditioning cannot provide heat.
Last time my cousin did this, and the next day the car just quit. The battery was completely drained, and the roadside assistance guy said deep discharging really shortens battery life—cost over 800 yuan for a new one. Worse, the cabin reeked of mildew. When the mechanic opened the AC lines, the evaporator was covered in mold. Now he triple-checks the AC knob before locking up—a lesson he’ll remember for a decade. Heads up: after turning off the engine, limit ventilation to 10 minutes max. Running the AC too long damages the car and wastes money, and you might end up paying big bucks to flush the entire AC system.
