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The forward cargo heat valve and vent valve are usually in opposite positions. If the forward cargo heat valve closes, vent valve opens.
The right ECSMC gives primary control of the valves when the airplane gets power, the left card gives backup control. When the airplane changes from air to ground, the card in control changes.
The ECSMCs control the valves through the EEUs in the P110 left power management power. The EEUs monitor for circuit malfunctions, open circuit breakers, failed relays, and valid current. If an EEU finds no malfunctions and gets an open command, it energizes the appropriate relay in the power management panel to open the related valve.
Limit switches (not shown) in the valves remove power from the valve’s motor when the valve gets to the commanded position. Limit switches in the valves give feedback directly to the appropriate ECSMC. The cards supply valve position data to each other on the ARINC 629 buses.
EFFECTIVITY BEJ ALL
Normal Control -Forward Cargo Heat Valve
On the ground, the valve usually moves between open and closed as ambient temperature changes. The forward cargo heat valve closes when the temperature at the TAT probe is more than 55F (13C), it opens when the temperature is less than 50F (10C). In the air, the valve usually stays open.
On the ground, the forward cargo heat valve will be open unless one of these conditions occurs:
*
Smoke is detected by the E/E cooling smoke detector

*
Forward cargo fire switch is set to ARMED

*
Equipment cooling switch is set to OVRD

*
Ambient temperature (TAT) is more than 55F (13C)

*
Ground test commands the valve to close.

In the air, the forward cargo heat valve is open unless one of these conditions occurs:
*
Smoke is detected by the E/E cooling smoke detector

*
Forward cargo fire switch is set to ARMED

*
Equipment cooling switch is set to OVRD.

Normal Control -Vent Valve
The usual position of the vent valve changes so that its position is the opposite of the position of the heat valve. For example, when the heat valve is open the vent valve is closed.
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A/C -EQUIPMENT COOLING -FWD CGO HT & VENT VLVS -FUNCTIONAL DESCRIPTION

The vent valve and the cargo heat valve can both be close if the forward cargo fire switch is set to ARMED.
*
Smoke is detected by the E/E cooling smoke detector

*
Equipment cooling switch is set to OVRD.

Fail Safe Control
The relays that supply power to the valves are set so that they always supply power to close the valves. This makes sure both valves close if the right and left ECSMCs have malfunctions.
Indication
Status messages show when a valve has a malfunction or the circuit that controls the valves has a malfunction.
The ECSMCs monitor information from the ELMS. This information helps the ECSMCs isolate malfunctions with the valves.
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A/C -EQUIPMENT COOLING -FWD CGO HT & VENT VLVS -FUNCTIONAL DESCRIPTION

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A/C -EQUIPMENT COOLING -OPERATION

General
An equipment cooling switch lets you set the desired mode of operation for the equipment cooling system.
Automatic Operation
The equipment cooling switch is an alternate-action switch. AUTO shows when you push the switch. This selects automatic operation (normal mode of operation) of the equipment cooling.
The OVRD light comes on when the override valve is in the OVRD position. The system puts the valve in the override position automatically or when the switch is out (non-normal mode of operation). The override mode gives cooling above a sufficient cabin differential pressure when the airplane is above 25,000 feet (7625 meters).
The override mode removes power to the supply and vent fans and sets the override valve to the OVRD position. This lets air vent from the supply part of the system overboard through the override valve. See the OVERRIDE MODE page in this section for more information on the override mode.
Ground Operation
Operation of the system on the ground normally does not require any inputs from you except to make sure that AUTO is selected.
If ambient temperature is equal to or greater than 110F (43C), you must supply conditioned air to the airplane.
Training Information Point
You can operate the system on the ground with a malfunction of the vent fan as long as ambient temperature is below 86F (30C). If the temperature goes above 86F (30C), then you must supply conditioned air to the airplane.
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