The 15454-FTA3-T fan-tray assembly is a removable drawer located at the bottom of the ONS 15454 front compartment that holds fans and fan-control circuitry. The front door of the ONS 15454 can be opened and left in place when removing or installing the fan-tray assembly. After you install the fan-tray assembly, you should only need to access it if a fan failure occurs or you need to replace or clean the fan-tray air filter installed beneath it.Fan speed is controlled by TCC+ card temperature sensors. The sensors measure the input air temperature at the fan-tray assembly. Fan speed options are low, medium, and high. If the TCC+ card fails, the fans automatically shift to high speed. The temperature measured by the TCC+ sensors is displayed on the LCD screen on the fan-tray assembly.