*
The override valve goes to the OVRD position which opens the supply duct to ambient

*
Cabin differential pressure pushes cabin air through the components and out of the airplane

*
The converter supplemental cooling fan comes on

*
The vent fan stops

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A/C -EQUIPMENT COOLING -FWD SYS -GENERAL DESCRIPTION -MECHANICAL
*
The forward cargo heat valve closes if it is open (low flow does not cause the valve to change position)

*
The vent valve opens if the forward cargo fire system is not armed. A low flow condition does not cause the valve to change position. The valve closes if the forward cargo fire system is armed.

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A/C -EQUIPMENT COOLING -GENERAL DESCRIPTION -ELECTRICAL

General
Equipment cooling control components supply automatic or manual mode selection (AUTO/OVRD), indications, and BIT for the system. These are the control components:
*
Equipment cooling switch

*
Left and right environmental control system miscellaneous cards (ECSMC)

*
Left and right equipment cooling controllers (ECC).

The equipment cooling switch gives indication for mode selection and lets you manually set the mode of operation to AUTO or OVRD.
The left and right ECSMCs give automatic control (AUTO or OVRD), indications (AIMS and equipment cooling switch), and BIT for the equipment cooling system. The cards control:
*
Which supply fan is primary and which is backup

*
When the supply and the vent fans operate.

*
The direction of air flow for the equipment cooling exhaust air. Directs the air to the cargo compartment for heating or vents the air overboard

*
When to set the system to the override mode

*
When to turn on the SATCOM cooling fan

*
When to give indications for mode selection and malfunctions.

The left and right equipment cooling controllers (ECCs) usually control the left and right equipment cooling supply fans and the override valve with inputs from the ECSMCs. The ECCs take control of the fans and valve if the airplane is in the air and the ECCs find low flow for an extended time (6.5 min in supply fan mode or 20 min in OVRD mode).
Interfaces
The ECSMCs have three types of input/output interfaces with system components and with other systems. One is through the left and right system ARINC 629 buses. These are the ARINC 629 interfaces:
*
OPAS

*
AIMS

*
ELMS.

The second type is through hard-wired inputs to ELMS. The third type is by hard-wired inputs/outputs from system components and the PSEUs 1 and 2.
See the INTERFACES page in this section for more information about the system components that are hard-wired to the ECSMCs.
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A/C -EQUIPMENT COOLING -INTERFACES

Left ECSMC Interfaces
The left ECSMC has hard-wire interfaces with these equipment cooling system components:
*
Duct pressure sensor for the E4-1, E4-2, and E4-3 shelves

*
Duct pressure sensor for the flight deck

*
Low (air) flow sensor for the main equipment center

*
Overheat switches for the left equipment cooling supply fan

*
Overheat switches for the equipment cooling vent fan

*
Open/close limit switches for the equipment cooling vent valve

*
Norm/ovrd limit switches for the left motor of the override valve

*
MEC equipment cooling low flow sensor

*
Left equipment cooling controller.

Right ECSMC Interfaces
The right ECSMC has a hard-wire interface with these equipment cooling system components:
*
Right equipment cooling controller.

*
Low (air) flow sensor for the flight deck

*
Open/close limit switches for the forward cargo heat valve

*
Norm/ovrd limit switches for the right motor of the override valve

*
Overheat switches for the right equipment cooling supply fan

*
Duct pressure sensor for the backup generator converter (E4-4 shelf)

*
Duct pressure sensor for the E5 equipment rack

Non Equipment Cooling ECSMC Interfaces
　
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