The Flex System Carrier-Grade chassis comes with two installed hot-swap fan logic modules.
The fan logic modules allow the Chassis Management Module to monitor the chassis fans. The fan logic modules must be installed in order for the Chassis Management Module to communicate with the fan modules and monitor fan presence, fan speed, and fan failures.
There is one fan logic module for each side of the chassis and it only allows communication to the fan modules on the same side of the chassis. You can replace a fan logic module without shutting down the chassis. The fans will not be monitored while the fan logic module is removed.
The following is an illustration of the fan logic module: