Troubleshooting the Cooling System

The router's cooling system comprises separate front and rear subsystems:

• The front subsystem includes the fan tray located behind the cable management system and the impeller located behind the craft interface. They cool the FPCs, PICs, and midplane. See Figure 1.
• The rear subsystem include upper and lower impellers in the rear of the chassis. They cool the SFMs, host module, PCGs, and power supplies. See Figure 2.

The cooling system draws in room air through the air intake vent located at the front of the chassis below the cable management system. After entering the chassis, the air stream separates into separate flows for the front and rear subsystems, and the MCS monitors the temperature of each flow independently. For a graphic depiction of the airflow, see Figure 20.

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. The MCS constantly monitors the temperatures detected by sensors on the midplane and router components, adjusting the speed of the fans and impellers as necessary. If the router temperature exceeds the acceptable maximum, the MCS turns off the power supplies. The following conditions automatically cause the fans and impellers to run at full speed and also trigger the indicated alarm:

• A fan or impeller fails (red alarm).
• One of the impellers is removed (yellow alarm).
• 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 Chassis and Interface Alarm Messages.

To troubleshoot the fans and impellers, follow these guidelines:

• If the red alarm LED on the craft interface lights, check the LCD on the craft interface for the source of the problem. The display reports the number of alarm conditions and the source of each alarm, as described in LCD Alarm Mode. For a list of messages, see Chassis and Interface Alarm Messages.
• Issue the following CLI command for more information about the source of an alarm condition:
  user@host> show chassis alarms
• If the blue OUTPUT OK LED on an enhanced power supply (or the amber NO AIRFLOW LED on an original power supply) is blinking, the airflow passing by the power supply might be insufficient. Place your hand near the exhaust vents at the rear of the chassis to determine whether the impellers are expelling air.
• If both power supplies have failed, the system temperature might have exceeded the threshold, causing the system to shut down. See All LEDs on Both Supplies Are Off.
• If the LCD on the craft interface reports failure of only one impeller and the other impellers are functioning normally, the impeller is probably faulty and needs to be replaced. For replacement instructions, see Replacing Hardware Components. For instructions about returning a faulty component to Juniper Networks, see Contacting Customer Support and Returning Hardware.