Cooling Units - Nortel Passport 15000 Hardware Description

126 Chapter 3 Shelf assembly

Cooling units

241-1501-200 5.2S2
Each Passport 15000 or 20000 has a cooling unit to maintain an ambient
temperature inside its shelf assembly. Maintaining the temperature at
optimum levels maintains the operation and performance of the switch
hardware. Keeping the shelf temperature within its normal operating range
will improve the system's service life.
When two Passport 15000 or 20000 switches are mounted into a NEBS 2000
frame, their cooling units are nested against each other. This integration
maximizes the use of hardware real estate. The cooling unit that operates with
the node in the bottom half of a NEBS 2000 frame is the lower cooling unit,
also known as the rear cooling unit because its fans face the rear of the switch
hardware and it is accessed from there. The unit that operates with the node
in the upper half is the upper cooling unit, also known as the front cooling unit
because its fans face the front of the switch hardware (where the processor
cards are) and it is accessed from there.
The versions of the lower cooling unit are NTHR51AA and AB while the
versions of the upper cooling unit are NTHR52AA and AB. Each cooling unit
has a modular design that enables field replacement of the whole unit or any
of its parts.
The physical versions of fans, fan controllers, and temperature sensors are
different depending which version of cooling unit you have. A replacement
part must match the part number that is identified in the tables "Cooling unit
parts for the AA versions" (page 378) and "Cooling unit parts for the AB
versions" (page 379).
The different versions of parts provide the same performance except the
shroud of the middle Dyna fan is shaped to reduce the overall noise level of
the lower or upper cooling unit NTHR51AB and NTHR52AB.
For the names and locations of the parts, see these figures:
• "Parts inside a lower cooling unit NTHR51AA (bottom shown upside
down)" (page 127)
• "Parts inside a lower cooling unit NTHR51AB (bottom shown upside
down)" (page 128)