Summer is just around the corner, and we are back with another burning question sent in by a reader: Will using the air-conditioner with the engine off damage my car?
It may be tempting to leave the air-conditioning on even while parked, but with the engine turned off, the air-conditioner’s compressor can’t rotate to pressurize the system. If the compressor is not spun by the engine’s fan belt, the system won’t work to cool the car cabin.
If you turn on the aircon blower fan, you will have air circulating inside the car, but it won’t provide the cooling benefit of the heat exchange between the condenser and the evaporator. The compressor provides pressure to these components of the aircon to move refrigerant from the hot side, also known as the condenser, to the cold side, called the evaporator. The refrigerant inside the sealed system is a hot, high-pressure liquid in the condenser where it receives cold air from the front of the vehicle and it turns to a low- pressure liquid in the evaporator, as it draws heat from inside the car with the help of the blower fan.
If you have the blower motor on with the engine off, you will be using up the car’s battery charge. Prolonged discharge of the battery may leave you stranded and unable to start the car because the starter motor requires a decent battery charge percentage.
Even with the engine off, recirculating air from just the fan with the windows open might be enough to cool the driver and passengers on a hot day. Don’t overuse it, though. You should turn on the engine so it can recharge the battery and turn the compressor at the same time. That way, the full cooling effect of the aircon can be enjoyed.