Why Does the Car Vent Blow Hot Air?
2 Answers
Reasons for the car vent blowing hot air: the external circulation is on, allowing hot air from the engine compartment to enter the cabin; or the external circulation is on and the temperature setting is for hot air. External circulation is on, allowing hot air from the engine compartment to enter the cabin: The car's air conditioning system has both internal and external circulation modes. Internal circulation draws air from inside the car, while external circulation draws air from outside. When driving, airflow enters the engine compartment through the front grille, creating positive pressure, which can force hot air from the engine compartment into the cabin through the external circulation intake. This results in hot air blowing from the vents. Solution: Turn off the external circulation. Note that in automatic air conditioning systems, the external circulation cannot be turned off in windshield defrost mode. If hot air is blowing but you can't turn off the external circulation, switch the vent position to any setting other than windshield defrost to disable the external circulation. External circulation is on and the temperature setting is for hot air: The car vents can blow either hot or cold air. The principle is simple: there is an air duct under the dashboard containing a heater core and an evaporator. The heater core is connected to the engine's cooling system and contains high-temperature coolant. The evaporator is part of the air conditioning system, where refrigerant evaporates to absorb heat and produce cold air. A baffle in the duct controls airflow—when cold air is selected, the baffle blocks the heater core, preventing airflow from being heated. When warm air is selected, the baffle opens, allowing airflow to pass over the heater core and be heated before entering the cabin. Solution: Turn off the external circulation or adjust the temperature knob to a cooler setting. Turning off the external circulation stops airflow, preventing hot air from blowing. Adjusting the temperature knob to a cooler setting ensures the baffle blocks the heater core, preventing it from heating the air.
Hot air blowing from car vents is a common issue when there's a problem with the air conditioning system. For example, the AC might not have switched to cooling mode - I've encountered this in many cars I've driven. Possible causes include the temperature setting being too high (with the knob in the red zone), or the AC simply not activating the cooling function, only blowing natural or warm air. Another factor could be insufficient refrigerant - leaks can cause system failure and prevent the compressor from running. Some vehicles experience stuck blend doors, which control the mix of hot and cold air; when stuck, only hot air comes through. High external temperatures and engine heat can also contribute. First, check your AC settings to ensure the correct mode is selected. If that doesn't help, have a professional inspect the refrigerant and compressor. Regular AC maintenance can prevent these issues proactively.