Troubleshooting the M120 Cooling System

Problem

The fans in a fan tray are not functioning normally. During normal operation, the fans in each fan tray function at less than full speed. The CB constantly monitors the temperatures detected by sensors and router components, adjusting the speed of the fans as necessary. If the router temperature exceeds the acceptable maximum, the CB turns off the power supplies. The following conditions automatically cause the fans to run at full speed and also trigger the indicated alarm:

• A fan fails (red alarm).
• One of the fan trays 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).

Solution

To troubleshoot the fans:

• If the red alarm LED on the craft interface lights, use the CLI to get information about the source of an alarm condition: user@host> show chassis alarms. For information about alarms, see M120 Alarm LEDs and Alarm Cutoff/Lamp Test Button.

  Use the CLI to check the status of the fans: user@host> show chassis environment. If the CLI output lists only one fan failure, and the other fans are functioning normally, the fan is most likely faulty and you need to replace the fan tray, as described in Replacing an M120 Fan Tray.

• Use the CLI to check the status of the fans. For example, you can issue the following command to get information about the source of an alarm condition:
  
  

  user@host> show chassis alarms

  For information about the alarms, see M120 Alarm LEDs and Alarm Cutoff/Lamp Test Button.

• Place your hand near the exhaust vents at the rear of the chassis to determine whether the fans are pushing air out of the chassis.
• If all power supplies have failed, the system temperature might have exceeded the threshold, causing the system to shut down.