Cooling System Operation - Cisco CRS-1 System Description

Chapter 3 Chassis Cooling System
The chassis has a replaceable air filter mounted in the front of the chassis in a slide-out tray above the
power shelf. The chassis air filter is shown in
You should change the air filter as often as necessary. In a dirty environment, or when you start getting
frequent temperature alarms, check the intake grills for debris and check the air filter to see if it needs
to be replaced.
See the Cisco CRS Carrier Routing System 4-Slot Line Card Chassis Installation Guide for the specific
Caution
air filter replacement procedure.
Figure 3-2
1 Chassis air filter
2 Air intake grille

Cooling System Operation

The fan control software and related circuitry varies the fan speed signal to individual fans to control
their speed. This increases or decreases the airflow needed to keep the system operating in a desired
temperature range. The chassis cooling system uses multiple fan speeds to optimize cooling, acoustics,
and power consumption.
At initial power up, the fans default to 4000 RPM. This provides airflow during system initialization and
software boot, and ensures that there is adequate cooling for the chassis in case the software hangs during
boot. The fan control software initializes after the routing system software boots, which can take three
to five minutes. The fan control software then adjusts the fan speeds appropriately, up to 7500 RPM.
During normal operation, the chassis averages the temperatures reported by inlet temperature sensors.
To determine the appropriate fan speed for the current temperature, the fan control software compares
the averaged inlet temperature to a lookup table that lists the optimal fan speed for each temperature.
The software then sets the fan speed to the appropriate value for the current temperature. To avoid
dynamic oscillation of the fan speed, the fan speed control is regulated in discrete steps.
OL-10805-10
Air Filter
Cisco CRS Carrier Routing System 4-Slot Line Card Chassis System Description
Figure 3-2.
3 Power shelf and power modules
4 Power shelf air filter
Cooling System Overview
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