Maintain the Impeller Assemblies

The router has two non-interchangeable impeller assemblies. The lower impeller is located behind the craft interface at the front the chassis (see Figure 1), and the upper assembly is located above the fan tray at the rear of the chassis (see Figure 2). They work together to cool the Packet Forwarding Engine components.

During normal operation, the impellers run at less than full speed. The following conditions automatically cause the impellers to run at full speed and trigger the indicated alarm:

• One of the impellers fails (red alarm).
• One of the impellers is removed (yellow alarm). For removal instructions, see the following sections:

• Remove the Lower Impeller Assembly
• Remove the Upper Impeller Assembly

• The router temperature exceeds the "temperature warm" threshold (yellow alarm).
• The temperature of the router exceeds the maximum ("temperature hot") threshold (red alarm and automatic shutdown of the power supplies).

For more information about impeller-related alarms, see Hardware and Interface Alarm Messages.

To check the status of the impeller assemblies, issue the show chassis environment command. The output refers to the Top and Bottom impellers, as shown in this example:

user@host> show chassis environment

Class Item                   Status     Measurement

 ...

Fans  Top Impeller           OK         Spinning at normal speed

      Bottom impeller        OK         Spinning at normal speed

 ...

For further description of the output from the command, see the JUNOS Internet Software Operational Mode Command Reference: Protocols, Class of Service, Chassis, and Management.