Some Apple products contain sensors that respond when they detect temperature changes inside your system or device, turning on fans to bring cooling airflow to critical components.
About fan noise
If your device's processor is working on intensive tasks – such as compressing HD video, playing a graphics-heavy game, or indexing the hard drive with Spotlight after you migrate data – the fans run faster to provide additional airflow. You might hear fan noise when this happens, especially if you're in a quiet environment. This rushing-air sound is a normal part of the cooling process.
Ambient temperature, the temperature outside the device, also plays a role in the fans' responsiveness. If the ambient temperature is high, the fans turn on sooner and run faster.
If you hear the fans in your Mac Pro running at full speed and you aren't performing any intensive tasks, check the enclosure. Make sure that your Mac Pro is locked and fully seated, or that the top cover or access door is closed and locked on rack-mounted models.
Make sure the vents on your Apple product aren't blocked
Some Apple products have vents that let fans bring in cool air and expel hot air. Make sure that the vents aren't blocked to allow your device to perform at its best.
- Apple TV 4K has a fan and a vent at the bottom.
- Airport Extreme and Airport Time Capsule have fans and vents at the bottom.
- iMac has vents along the bottom edge and on the back.
- iMac Pro has vents along the bottom edge and on the back.
- Mac mini has vents at the bottom to bring in cool air from beneath the device and vent hot air from the back.
- Mac Pro has three fans on the front of the computer and vents on the front and back.
- MacBook Pro has vents along the side and on the back. MacBook Air computers have vents along the back near the clutch.
The surface your device rests on can block its vents, affecting fan behaviour. If you use your device on a soft surface like a couch, pillow, bed or your lap, its fans might run more. Using your device on a hard, flat surface like a table or desk is best for temperature control.
If the fans in your Mac run fast even when it isn't experiencing heavy usage and is properly ventilated, you might need to reset the System Management Controller (SMC) on your Mac. If you're experiencing this issue on an Apple TV 4K, Airport Extreme, or Airport Time Capsule, unplug the device, then plug it back in.
Learn more about the operating temperature of Apple notebook computers.