Juniper MX2020 Hardware Manual page 70

WARNING:
completely.
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, (see Figure 21 on page
Figure 21: Airflow Through the Chassis
Upper Fan trays
Card cage
Card cage
Airflow divider
Card cage
Lower fan trays
The MX2020 router provides a two-stage front-to-back cooling system. Air is pushed into the bottom
inlet and up through the lower fan tray, and exits through the opening between the backplanes in the
center of the chassis. This cools the bottom MPCs, half of the SFBs and CB-REs. Air is pulled through the
SFBs and all the CB-REs in the center of the chassis and is exhausted out the upper rear of the system.
Before removing a fan tray, make sure the fan blades have stopped
46).
Power
supply
cooling
46