Juniper EX9253 Hardware Manual page 32

Figure 9: Faceplate of the Fan Tray
1 Captive screw
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2 Latch
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The fan trays and power supplies are hot-removable and hot-insertable field-replaceable units installed
in the rear panel of the switch. You can replace them without powering off the switch or disrupting
switch functions. In a switch powered by AC power supplies, a minimum of two high line power supplies
or three low line must be installed in the switch for non-redundant operation. To ensure proper
operation of the switch, you must install a replacement power supply shortly after removing a power
supply from the chassis. To maintain proper cooling, you must install a replacement fan tray or a blank
panel in the fan tray slot shortly after removing a fan tray from the chassis.
The switch monitors the temperature of switch components. Under normal operating conditions, the
fans in the fan trays run at less 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 line card that cannot be cooled adequately is
disabled. If the fire threshold temperature is exceeded, the Routing Engine shuts down the system by
disabling output power from each power supply. You cannot replace a single fan. If one or more fans fail,
you must replace the entire fan tray.
3 Status LED
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