Why does the car still blow hot air when the AC is turned on?
4 Answers
Reasons why the car still blows hot air when the AC is turned on: Incorrect use of zoned air conditioning. More information about zoned air conditioning is as follows: 1. Zoned air conditioning refers to the ability to independently adjust the temperature in different areas within a car cabin. For example, dual-zone air conditioning means the temperature on the left and right sides of the car can be adjusted independently; four-zone air conditioning means the temperature in the front and rear rows, as well as the left and right sides, can be adjusted independently, meaning there are four zones where the temperature can be independently controlled. 2. Automatic zoned air conditioning consists of four parts: first, the sensor part, which is responsible for temperature information feedback; second, the system's 'control center,' which is the air conditioner control unit ECU; third, the control components; and fourth, the self-check and alarm part.
I had the same issue with my old Tiguan before, the air blowing from the AC was scorching hot! Turned out the temperature blend door actuator was stuck when I took it to the repair shop. The mechanic said this mechanism is located deep inside the dashboard and tends to get sticky from long-term disuse. If it gets stuck in the heating position, all the air from AC will be preheated by the heater core. Also, check if the AC pressure lines feel hot to touch? If the pipes are hot, it means the refrigeration system isn't working at all - either the refrigerant has leaked out or the compressor isn't functioning. Another method is to directly test the MAX COOL function in your car. If that doesn't work either, it's most likely a mechanical failure.
This situation can really make people faint from the heat in summer! The most likely culprit is the blend door actuator motor, which may be stuck in the heating position and unable to move. You can try setting the temperature to the lowest and listen for any buzzing sound from the motor near the airbox. If there's no sound, it's almost certain that it's broken. Another hidden cause could be a stuck thermostat leading to excessively high coolant temperature, causing heat to directly enter the heater core. Also, remember to check if the cabin air filter is clogged like a rag—an extremely dirty filter can prevent fresh air from being drawn in. Recently, several cars I've serviced had issues with low refrigerant levels and failed compressor clutches, causing the entire system to collapse. It's advisable to check the high and low pressure readings.
When the AC blows hot air, quickly feel the AC pipes inside the dashboard! If the low-pressure pipe is icy cold, it's a problem with the blend door flap. If it's hot, the refrigeration system has failed. A common cause is a burnt-out compressor clutch coil—if you don't hear the solenoid click at all when pressing the accelerator, it's likely the culprit. Some models also have a heater valve stuck in the open position, allowing hot coolant to continuously heat the heater core. Last time, while helping a neighbor diagnose their car, it turned out to be poor contact in the AC pressure switch, causing the system to falsely detect high pressure and lock the compressor. It's best to read the fault codes before proceeding.
