Juniper ACX5048 Hardware Manual page 61

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Both the 1 U and 2 U versions of ACX5000 fan modules have a similar design with different dimensions.
The 1 U ACX5000 routers have 5 fan modules numbered 0 through 4 from left to right, where the 2 U,
ACX5096 has 3 fan modules numbered 0 through 2. On all ACX5000 routers, each fan module slot has a
fan icon next to it.
Figure 13 on page 61 shows the 1 U fan module and Figure 14 on page 61 shows the 2 U fan module.
Figure 13: 1 U Fan Module Used in ACX5048
Figure 14: 2 U Fan Module Used in ACX5096
You remove and replace a fan module from the FRU end of the chassis. The router continues to operate
for a limited period of time (30 seconds) during the replacement of the fan module without thermal
shutdown.
NOTE: All fan modules must be installed for optimal operation of the router.
The fan module airflow direction (port-to-FRU, AFO) is indicated by either a gold color or the label AIR
OUT . Table 13 on page 62 lists the fan module product SKUs and the direction of airflow in them: