The AT-SBxFAN12 module is the cooling unit for the chassis. It is a field-replaceable assembly that is factory installed and shipped with the AT-SBx8112 chassis. The module is controlled by the AT-SBx81CFC400 controller fabric card. The fan speeds are automatically adjusted according to the internal operating temperature of the switch. The fans are at their lowest speed when the ambient temperature coming into the fan is approximately 20° C. The fan speeds increase to provide additional cooling as the ambient temperature rises.