Figure 17: Airflow Through Chassis; Figure 18: Fan Tray - Juniper MX240 Hardware Manual

Chapter 2: Hardware Components
The air intake to cool the chassis is located on the side of the chassis next to the air
filter. Air is pulled through the chassis toward the fan tray, where it is exhausted out
the side of the system. The air intake to cool the power supplies is located in the
front of the router above the craft interface. The exhaust for the power supplies is
located on the rear bulkhead power supplies.

Figure 17: Airflow Through Chassis

The host subsystem monitors the temperature of the router components. When the
router is operating normally, the fans function at lower than full speed. If a fan fails
or the ambient temperature rises above a threshold, the speed of the remaining fans
is automatically adjusted to keep the temperature within the acceptable range. If the
ambient maximum temperature specification is exceeded and the system cannot
be adequately cooled, the Routing Engine shuts down the system by disabling output
power from each power supply.

Figure 18: Fan Tray

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Cooling System