What is the working principle of a vehicle cooling fan?
3 Answers
The working principle of a vehicle cooling fan is: The air conditioning computer receives signals from the air conditioning pressure switch, indoor and outdoor temperatures, and then transmits these signals to the engine computer via the bus. When the engine receives the signal to activate, it controls the compressor and cooling fan relay to engage. When the air conditioning pressure increases due to environmental and internal factors, the engine computer receives the signal from the air conditioning computer and controls the high-speed relay of the cooling fan to engage, causing the cooling fan to operate at high speed. The vehicle engine radiator consists of three parts: the inlet chamber, the outlet chamber, and the radiator core. The coolant flows inside the radiator core, while air passes outside the radiator. The hot coolant cools down as it dissipates heat to the air, and the cold air warms up by absorbing the heat dissipated by the coolant.
The cooling fan acts as the car's thermostat, its operation entirely dictated by the coolant temperature sensor. When the antifreeze temperature exceeds approximately 95°C, the ECU receives an alert and immediately energizes the fan relay. Once the fan motor kicks in, it drives the blades to whirl and draw air. Interestingly, some vehicles are equipped with dual-speed fans—operating at low speed when the temperature first exceeds the threshold, then switching to high speed with a roar if traffic congestion causes the coolant temperature to continue rising. Older cars are even more fascinating, featuring a silicone fluid clutch fan mounted in front of the radiator. The higher the temperature, the more viscous the silicone fluid inside becomes, causing the fan to lock and spin faster. When the fan operates, airflow rushes through the radiator fins, dissipating the scorching heat from the antifreeze into the air. I recall once driving on a mountain road when the AC suddenly cut out. Glancing down, I saw the temperature gauge nearing the red zone—turned out the fan fuse had blown. Had I not noticed in time, the engine would've surely overheated.
Here's a hot tip for you: even cooling fans now come with smart dual-mode functionality. During normal driving, it operates as quietly as a librarian, but once you hit traffic or start climbing a hill, the temperature gauge needle jumps up, and the fan instantly switches to beast mode, making noise like a hair dryer on its highest setting. The principle is actually quite simple—it relies on the temperature switch on the radiator's lower hose: at 90°C, the metal strip inside bends, connecting the low-speed circuit; if it hits 105°C, the strip fully bends with a snap, engaging the high-speed mode at full power. Newer models are even more impressive, featuring PWM-modulated fan motors for stepless speed control. Once, while repairing a car, I encountered a bizarre issue where the fan wouldn’t stop running. Turned out the A/C pressure switch was short-circuited, falsely sending a high-temperature signal to the ECU, causing the fan to run wild for three hours and draining the battery dry.
