NEC A1160 - Manual (Page 32)

Cooling
2-14
Cooling
Each cell is cooled by two fan modules. Each fan module contains two 12-volt
high-performance fans that provide the airflow required to cool the cell components and
processors. The fan modules are mounted in the front of the cell.
Note: The power supplies within the cell are self-cooled.
The fans have four speeds. The system automatically adjusts fan speed based on the
ambient and system component temperatures or under certain failure or maintenance
conditions. If a fan fails or is removed, the system switches the remaining fans in the cell
to high speed. The fans return to their normal speed when the failure condition is
resolved.
The cooling system is n+1 redundant; that is, it can tolerate the failure of one fan. If two
fans fail, the cell powers down. If a fan module is removed, the master power control
turns off power to the cell after 2 minutes. This allows time for the fan or memory to be
replaced.
The fans have a green LED that is on when the fan module is functioning properly. The
green LED is off on a faulty fan module or if DC power is not applied to the cell. A fan
module can be replaced by a customer.
Figure 2-11 shows the location of the fan modules on the front of the cell.