Why is hot air coming out of the vents when the air conditioning is off?
2 Answers
Hot air coming out of the vents when the air conditioning is off is because the vehicle is set to external circulation. When the external circulation mode is activated, air is drawn from outside, and the air intake vent remains open. As the vehicle moves, the pressure difference causes outside air to flow into the cabin. Since the engine temperature rises, this incoming air feels warm. Simply turning off the external circulation will stop this phenomenon, which is completely normal. Generally, a car's heating system doesn't rely on the air conditioning's heating mode. Instead, warm air from the engine's cooling system is filtered and directed into the cabin. When the temperature control knob or switch is set to the heating position, the heating vent opens, allowing warm air to naturally enter the cabin.
I've been driving for over a decade and often encounter the annoying situation where hot air still blows from the vents when the AC is off. This mainly happens because the fan is set to external air intake mode, drawing outside air through the engine compartment into the cabin—especially noticeable during hot summers. Another common cause is coolant flowing through the heater core in the heating ducts, where valves may not seal properly or get stuck, allowing hot air to escape. I remember one long trip where this made the cabin heat up quickly and even increased fuel consumption. My advice is to first press the recirculation button to switch to indoor air, avoiding external heat. If that doesn't work, check the position of the temperature control knob or if the ventilation ducts are aging. Don't underestimate this issue—over time, it affects driving comfort. I recommend having technicians inspect valves and flaps during regular maintenance to ensure the system functions properly.
