Cooling System - Juniper M40 Hardware Manual

Cooling System

The cooling system consists of separate subsystems (sets of fans and impellers) that draw
room air into the chassis to keep its internal temperature below a maximum acceptable level.
When the temperature is below the maximum, the fans and impellers function at less than
full speed. If sensors detect that the temperature of a component has exceeded the
acceptable maximum—for example, because an impeller is removed—the speed of the
remaining impellers and fans is automatically increased to reduce the temperature. The fans
and impellers can function at the higher speed indefinitely.
For more information about the cooling system, see the following sections:
Cooling System Components
The cooling system has the following components. Except as noted, they are hot-removable
and hot-insertable, as described in "Field-Replaceable Units (FRUs)" on page 4.
Cooling System Components on page 23
Airflow through the Chassis on page 24
Air intake vent and air filter—Provide an opening for room air to enter the router. They
are located at the bottom of the chassis front, below the craft interface, as shown in
Figure 1. The air filter prevents dust and other particles from entering the cooling
system. For replacement instructions, see "Maintain and Replace the Air Filter" on
page 154.
Do not remove the air filter for more than a minute or so
while the router is operating. The fans and impellers are
powerful enough to draw in foreign material, such as bits
of wire, through the unfiltered air intake, which could
damage router components.
Upper and lower impeller assemblies—Cool the Packet Forwarding Engine components
(backplane, SCB, FPCs, and PICs). The lower impeller assembly is located behind the
craft interface at the front the chassis, and the upper assembly is located above the fan
tray at the rear of the chassis. Each assembly houses two impellers for redundancy. The
assemblies are not interchangeable. For replacement instructions, see "Replace the
Lower Impeller Assembly" on page 158 and "Replace the Upper Impeller Assembly" on
page 159.
Fan tray—Cools the Routing Engine and backplane. The tray houses three fans for
redundancy and is located above the Routing Engine at the upper rear of the chassis (see
Figure 2). For replacement instructions, see "Maintain and Replace the Fan Tray" on
page 155.
Power supply integrated fan—Cools the power supply. It is not field-replaceable.
Cooling System
Hardware Component Overview 23