Why is hot air coming out of the vents when the AC is off and it feels hot to the touch?
2 Answers
Hot air coming out of the vents when the AC is off and feeling hot to the touch is due to the automatic air conditioning system switching to external circulation or foot mode to ensure air circulation inside the cabin even when turned off. The negative pressure generated inside the vehicle while driving causes air to enter the AC system through external circulation, creating free convection. This effect becomes more noticeable at higher speeds, which is why you may feel hot air coming from the vents even when the AC is off. This is a normal phenomenon. Car air conditioning refers to the air conditioning device installed in vehicles, which can cool, heat, ventilate, and purify the air inside the cabin, providing a comfortable environment for passengers, reducing driver fatigue, and improving driving safety. The presence of an air conditioning system has become one of the indicators of a fully functional car.
I've been driving for over a decade and often encounter this situation where hot air blows from the vents even when the AC is off. To put it simply, most of the time it's because I left the external circulation mode on, allowing hot outside air to enter through the ducts. The engine compartment gets extremely hot, especially in summer or during traffic jams, and this heat can sneak in with the airflow. Additionally, if the fan knob isn't completely turned off, or if there's an issue with internal valves—like a stuck blend door—then hot air can directly enter the cabin. I've also experienced older cars with aging AC systems where poor seals caused hot air leakage. My advice is to first check if the circulation button is switched to internal recirculation when you start the car, ensure the fan is fully off, and test it on a short trip if necessary. If the problem persists, it's best to have a professional shop inspect for any damage to the valves or ducts—don't ignore it, as it can affect driving comfort.
