What to Do When the Car Air Conditioning Isn't Heating?

[VanColeman]

It is recommended to check the heater core for any blockages. If found, replace the heater core. It is suggested to clean or replace it as necessary. It is advised to visit a 4S shop to replace the new component.

[DelRebecca]

My old Jetta had this issue last winter too - the AC was blowing cold air. First thing I checked was the coolant reservoir, and sure enough the level was below the minimum mark. When engine coolant temperature is insufficient, it can't properly heat the cabin - that's basic knowledge. You'd better check the inlet and outlet hoses of the heater core after warming up the car. If there's significant temperature difference between them, it indicates poor circulation. If the hoses feel soft, the thermostat might be stuck open - replacing it only costs about 100 yuan. By the way, never top up low coolant with plain water - the changed freezing point could crack the radiator. I once took the easy way out by adding tap water, and ended up with three cracks in the radiator come winter - 800 yuan repair bill that I still regret to this day.

[KateLynn]

Last week, I helped my mother-in-law check her little 'Polo.' Even with the AC set to 28°C, it was still chilly. Turned out the MAX button on the AC panel was lit—this button locks the temperature at the lowest setting. And for those who always keep it on external circulation, the engine heat just can’t get in. I taught her to press the AUTO and ECON buttons simultaneously for three seconds to reset the AC computer, and warm air started flowing immediately. Nowadays, new cars come with over a dozen buttons, more complicated than smartphones. My dad has been driving a GL8 for three years and still doesn’t know where the front defogger button is.

[Avery]

A repair shop mechanic told me a truth: out of ten cars with weak heating, six have air filters clogged like quilts. Last week, an Q5 came in, and when we opened the air filter, it was full of willow and poplar catkins—the airflow was weaker than blowing out a candle. After replacing the filter, the heating became scorching hot in just five minutes. Changing the filter yourself is super easy—just pop open the glovebox on the passenger side. An OEM filter costs around a hundred bucks. Remember, don’t cheap out and buy no-name filters. I’ve seen cars with moldy filters growing green fuzz—the smell was like boiling stinky rags with socks.

[Emmett]

A friend's modification shop had an even more bizarre case: a Mercedes-Benz had heating that kept switching between cold and hot. Upon dismantling the dashboard, they found the linkage of the blend door actuator broken. That tiny plastic piece was only the size of a fingernail, and after breaking, the flap fluttered randomly, blowing cold air to the face while hot air came out at the feet. Nowadays, cars use servo motors to control the flaps, and if a resistor fails, the system just stops working. Last week, they dealt with a Honda CR-V's computer error code where the AC system mistook 22 degrees for minus ten degrees, going into overdrive with cooling. That kind of issue requires connecting to the computer to recalibrate the sensors.

[VonDaisy]

The auto repair shop technician taught me a four-step troubleshooting method: First, rev the engine to 3000 RPM while stationary. If the air vents warm up within two minutes, it indicates a water pump issue. Then, feel the heater hose near the accelerator pedal—if it's hot, check the blower and air ducts. Next, switch between internal and external air circulation to listen for the sound of the flap motor. Finally, read the computer data stream to check the accuracy of the temperature sensor. A special reminder for EV owners who have modified their heater valves: Last winter, five Teslas experienced heating failures due to incorrectly installed three-way valves, with disassembly and reassembly costs three times higher than the valve itself.