Why does the car's fan keep running after the AC is turned off?

[VanLeilani]

Car's fan keeps running after the AC is turned off because the fan coil circuit is not connected to the compressor (i.e., not connected to the AC system), but rather to the engine. The fan not only cools the compressor but also dissipates heat for the engine. Below is an introduction to the four circulation processes of the AC system: 1. Compression process: The compressor inhales low-temperature, low-pressure refrigerant gas from the evaporator outlet and compresses it into high-temperature, high-pressure gas before discharging it. 2. Heat dissipation process: The high-temperature, high-pressure superheated refrigerant gas enters the condenser, where, due to the reduction in pressure and temperature, the refrigerant gas condenses into liquid and releases a large amount of heat. 3. Throttling process: The higher-temperature and higher-pressure refrigerant liquid passes through the expansion device, causing its volume to increase, and its pressure and temperature to drop sharply, discharging as a mist (fine droplets). 4. Heat absorption process: The mist-like refrigerant liquid enters the evaporator, where, since the boiling point of the refrigerant is much lower than the temperature inside the evaporator, the refrigerant liquid evaporates into gas.

[VonLuke]

I've also experienced the issue where the fan keeps buzzing after turning off the AC in my car, which feels quite strange. It might be due to a stuck fan relay or a faulty thermostat. The fan is designed to help cool the engine and should stop when the AC is turned off. However, if there's a short circuit or a sensor malfunction, it may continue running. If this persists, it can drain the battery, accelerate its aging, or even trigger an overheating warning. Once, I encountered this problem and drove straight to the repair shop. They found that the relay contacts were burnt out, and replacing the part cost me a little over a hundred yuan. I recommend not ignoring small issues—regularly check the fan system to keep your car running smoothly, especially during hot weather when you need to pay extra attention to cooling.

[McEmery]

As someone who often helps out at car shops, I think if the fan is off but the AC is still running, it's mostly an electrical control issue. For example, a fault in the fan motor circuit or a malfunctioning temperature sensor signal could cause the fan to keep running due to a false high-temperature signal. This isn't a major problem, but ignoring it can easily drain power or affect the lifespan of other components. I recommend first checking if the fan fuse is blown or if the plug connections are loose. If the fan sounds abnormal, the motor might be worn out and need replacement. Related repairs usually cost a few hundred yuan, so timely action can prevent more serious consequences. Regularly cleaning the cooling system during car maintenance can help prevent such awkward situations.

[ElisaDella]

A fan that won't stop running sounds annoying, but it may indicate potential safety hazards. When the fan continues operating after turning off the AC, it's often due to a failed thermostat in the cooling system or a stuck fan controller. This wastes battery power and increases overheating risks. When this happens, I recommend parking as soon as possible to check if the coolant level is normal, avoiding long-distance driving that could worsen the situation. If the issue recurs, have a professional technician use a multimeter to diagnose wiring abnormalities. For safety, avoid disassembling the fan circuit yourself to prevent electric shock or improper operation. Developing a monthly habit of checking the fan's condition can help reduce unexpected surprises.