Most computers including notebooks and netbooks run cool over their life, but some occasionally begin to run increasingly warm and may exhibit unpredictable behaviors such as shutting down, locking up, or going to sleep (suspend). Often in laptops, these symptoms may be caused by dust and lint build up clogging the heat sink and loading up the fan blades, adding drag and reducing airflow. Systems operated in especially dusty environments may need more frequent cleaning, and as some systems draw air in from the bottom, if they are often operated on a bed or other fabric surface, they are more likely to draw in dust and lint fibers which wind up blocking air flow through the heat sink. This is like blocking off the flow of air to your car's radiator.
In the picture to the left, the amount of dust and lint build up on the fan blades and housing themselves are only part of the problem. Note how the rectangular heatsink fins to the left of the fan are clogged up. The fan on this system likely ran more often and at a higher speed than would normally be required to keep the system cool. A fan running at higher RPMs is louder, and consumes more battery power, thus decreasing run time between charges. Cleaning the fan and heatsink with compressed air from a can will help to restore efficiency and performance levels. For the benefit of those that haven't spent much time poking around inside a laptop, it may be helpful to consider how the laptop is cooled and why this is important. The cooling system in most laptops consists of heat sink assemblies that attach to the CPU and GPU and connect via copper heat pipes to an array of metal fins which provide a greater amount of radiant surface area. The cooling fan draws in air through vents in the side or bottom of the system and exhausts it out through these fins. As the cooler air passes over and between these fins, it draws away the heat. Some laptop system designs mount the fan separately from the heat sink assembly as in the picture above, while others integrate he fan and heatsink / heat pipe assemblies together as in the example below. The photos below represent top and bottom views of the same fan. Note the two flat heat pipes, each leading to a separate set of cooling fins (the two rectangular projections seen more clearly at the 12 and 3 o'clock positions in the photo on the right). The grey foam bits help to seal the fan assembly to the case and ensure all the air goes through the fins rather than escaping around them.
Integrated fans of this type should not be removed from the system unless they are being replaced because removing them necessitates a substantial amount of system dis-assembly and the attached heatsinks are also detached from the CPU and GPU in the process. I would recommend this type of repair be performed by an authorized servicer, or by a highly skilled user on systems that are outside the manufacturer's warranty. With the system off, compressed air from a may be blown in through the heat sink fin area, and also directed to clean the blades of the fan with the fan still installed in the system. For systems with a fan mounted independent of the heatsink and cooling fin assembly, removal of the fan is usually easier and allows more thorough cleaning. I'm going to do a quick walk through on an example system, but will offer the disclaimer that this should only be attempted by an authorized servicer under warranty, and by experienced users outside of warranty. This particular model draws air in through the bottom of the unit. The fan can be easily accessed after removing two screws from the fan cover on the bottom of the system. Note battery and AC are removed before performing any work.
After loosening / removing these two screws, the cover can be lifted off and removed.
Locate and remove the screws that hold in the fan. It helps to have a magnetic screw driver. Unplug the fan power connector from the system board and lift the fan out carefully. The system I used for these photos was clean and well cared for. However the following picture illustrates a similar system that is exceptionally clogged with dust. Note that the build up will be most evident on the inside of the fin area and may not always be visible looking at the external vents on the system.
Directing compressed air from the outside in, will clear away all this dust. It is important to clean out the fan as well, using a finger to keep the blades from spinning while cleaning them. When all is clean and carefully reassembled, the system should return to cool running.
So, if your system runs warmer than it used to, or your fan seems to run at a higher speed and more frequently than when the system was new, dust and lint build up in the cooling fins and fan may be to blame. A careful bit of preventative cleaning once a year should help your laptop keep it's cool.