Juniper MX10004 - Page 40

The system connually monitors the temperature of crical parts across the chassis and adjusts the
chassis fan speed according to the temperature. Junos OS controls the fan speed. Under normal
operang condions, the fans in the fan tray run at less than full speed. If one fan tray controller fails or
appears missing , the other fan tray controller sets the fans to full speed. (A fan tray can appear to be
missing when you replace an SFB, for example.) The ability to modify fan speed enables the router to
connue to operate normally as long as the remaining fans cool the chassis suciently. Use the show
chassis fan command to see the status of individual fans and fan speed.
To determine the cooling of all the components in the system, use the show chassis environment command.
Airow Direcon in the MX10004
The air intake to cool the chassis is located on the port (line card) side of the chassis. Air ows into the
chassis from the ports in the Roung and Control Boards (RCBs) and line cards, through the Switch
Fabric Boards (SFBs), and exits from the fan trays and the power supplies. See Figure 16 on page 30.
Figure 16: Airow Through an MX10004
The fan tray connues to operate indenitely and provide sucient cooling even when a single rotor
fails, provided the room temperature is within the operang range. You can check the status of fans by
viewing the LEDs on each fan tray.
You cannot replace a single fan. If one or more fans fail, you must replace the enre fan tray.
In addion to the fans in the fan trays, an internal fan in each power supply also helps to cool
components such as line cards.
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