The behavior you described, where the radiator fan turns on only when you activate the AC and then goes off almost immediately, is likely normal and part of your car's cooling system design. Let's break down how the cooling system works and why this happens:
Cooling System Overview: The cooling system in a car is responsible for maintaining the engine's operating temperature within a safe range. It prevents the engine from overheating, which could lead to significant damage. The main components of the cooling system include the radiator, water pump, thermostat, and radiator fan.
Radiator Fan: The radiator fan's primary purpose is to draw air through the radiator to help dissipate heat from the engine coolant. It is typically controlled by a temperature-sensitive switch or a relay that monitors the engine's coolant temperature.
AC Compressor: When you turn on the AC, the air conditioning system activates the AC compressor. The AC compressor puts an additional load on the engine as it runs, generating extra heat.
Now, the reason why the radiator fan turns on when you activate the AC is that the AC system generates extra heat that needs to be dissipated to prevent the AC components from overheating. When you turn on the AC, the additional heat from the AC compressor increases the coolant temperature slightly, triggering the fan to turn on.
However, since the AC system doesn't produce as much heat as the engine itself, the temperature increase is relatively small. As a result, the fan doesn't need to run for an extended period to cool down the engine coolant, and it goes off almost immediately after you turn off the AC.
In summary, the behavior you're experiencing is likely normal and part of the cooling system's design. The radiator fan turns on when you activate the AC to help dissipate the extra heat generated by the AC system, and it goes off quickly since the temperature increase is not significant enough to warrant continuous operation of the fan. If you notice any drastic temperature fluctuations, prolonged fan operation, or other signs of cooling system issues, it's best to have your car inspected by a qualified mechanic to ensure everything is working correctly.