AIRPLANE
OPERATIONS
MANUAL
PNEUMATICS
AIR CONDITIONING
AND PRESSURIZATION
JUNE 29, 2001
2-14-20
Page
1
Code
01
ELECTRONIC BAY COOLING SYSTEM
FORWARD ELECTRONIC BAY
An automatic cooling system is provided in the nose electronic bay,
where most of the electronic equipment is installed. This system
maintains the temperature inside the bay within the avionics
operational limits.
The system comprises two NACA air inlets, two shutoff valves, two
recirculation fans, two exhaust fans, two check valves, four control
thermostats, and two overtemperature thermostats.
The NACA air inlets are provided with water separators and drains to
deter water ingestion by the air inlets into the compartment.
All the fans are powered by four dedicated Inverter Modules.
When the airplane is energized, the inverter modules are turned on,
supplying power to the recirculation fans.
The electrical power supply to the recirculation fan 2, exhaust fan 1
and shutoff valve 1 is completely segregated from the remaining
components, to prevent a total loss of the system in case of an
electrical system single failure. Each recirculation fan operates
continuously when its associated bar is energized.
A check valve is installed on each exhaust duct (left and right) to avoid
water ingestion through the exhaust fans.
If the forward electronic bay internal temperature exceeds 24°C (75°F)
the control thermostats open the shutoff valves and turn the exhaust
fans on. When the temperature drops below 19°C (66°F), the shutoff
valves are closed and the exhaust fans are turned off.
In the event that the temperature limit is reached, two overtemperature
thermostats are actuated and a caution message is presented on the
EICAS.
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