Troubleshoot the Cooling System
The router's cooling system comprises two separate subsystems:
- Upper and lower impeller assemblies—Cool the Packet Forwarding Engine components (backplane, SCB, FPCs, and PICs). The lower impeller assembly 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). Each assembly houses two impellers for redundancy. The assemblies are not interchangeable.
- Fan tray—Cools the Routing Engine and backplane. The tray houses three fans for redundancy and is located above the Routing Engine at the upper rear of the chassis (see Figure 2).
The cooling system draws in room air through the air intake vent located at the front of the chassis below the craft interface. After entering the chassis, the air stream separates into separate flows for the front and rear subsystems, and the temperature of each flow is monitored independently. For a graphic depiction of the airflow, see Figure 10.
For the cooling system to function properly, the clearance around the chassis must be sufficient for unobstructed airflow. See Clearance Requirements for Airflow and Hardware Maintenance.
During normal operation, the impellers and fans in the fan tray function at less than full speed. Sensors on the backplane and router components constantly monitor their temperature, and the speed of the fans and impellers is adjusted as necessary. If the router temperature exceeds the acceptable maximum, the JUNOS software shuts down the router by turning off the power supplies.
To troubleshoot the cooling subsystems, follow these procedures: