One of the more important components in the power supply is one that seems tangential to it: the power supply fan. Since the earliest PCs, the power supply fan has been the primary cooling source for the entire Pc. Today's PCs, of course, incorporate additional cooling methods, including auxiliary fans and CPU cooling devices, but the power supply fan remains an important factor in the overall cooling equation. The fan is traditionally located at the rear of the power supply, and special vents are provided for it in the case of the supply itself to allow for it to exhaust. Most fans use + 12 V power to operate, despite the fact that the wires that run to them are normally red for the + 12 V line, and black for the ground. In addition to the regular fan found in the power supply, most newer systems include auxiliary fans for improved air flow and system cooling. These are typically mounted at various venting locations around the outside of the system case. The standard size of a PC cooling fan is about 3.25" or 80 mm square, but they come in other sizes as well.
The fan is the component most likely to go first in a power supply. The usual cause of this is dirt that gets into the motor of the fan and gums up the works. The average time until failure is greatly increased if the PC is used in a very dirty or dusty environment, m if the PC:: is never cleaned. When the fan stops working, overheating of the components within the power supply as well as in components in the rest of the PC are likely. To overcome this problem you can use a PC that makes use of the optional fan monitoring signal and can detect a fan failure and sound an alarm to the user, or shut down the Pc. Another way of detecting an overheating condition is through hardware that monitors the internal temperature of the system. The power supply fan is probably the only component that can be replaced by an end-user.