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Troubleshoot the Fan Tray

The fan tray installed along one side of the chassis houses four fans that draw room air into the chassis to maintain an acceptable operating temperature for the Routing Engine, PICs, FEB, and other components. For a graphic depiction of the airflow, see Figure 10.

For the fan tray to function properly, the clearance around the chassis must be sufficient for unobstructed airflow. See Clearance Requirements for Airflow and Hardware Maintenance.

Temperature sensors on the components detect temperatures above the acceptable range. Fan failure or an excessive temperature condition triggers the red alarm LED on the craft interface. If the temperature passes the acceptable maximum, the Routing Engine shuts down the router by turning off the power supplies.

To troubleshoot the fan tray, follow these guidelines:

Check the status of the fans in the fan tray by issuing the show chassis environment command. The output includes an entry for each fan, as shown in this example:
user@host> show chassis environment
```
Class Item             Status  Measurement
...
Fans  Left Fan 1       OK      Spinning at normal speed
      Left Fan 2       OK      Spinning at normal speed
      Left Fan 3       OK      Spinning at normal speed
      Left Fan 4       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.
If the fan tray fails, determine whether you can distinguish individual blades in a fan—this is not possible when the fans are rotating at normal speed.

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