*
Forward cargo heat valve
*
Vent valve
*
Air filter
*
Supply fan (2)
*
Override valve
*
Duct pressure sensor (4)
*
Low flow sensor (2)
*
Converter supplemental cooling check valve
*
Equipment cooling controller (2) (not shown).
The left and right ECS miscellaneous cards (ECSMCs) (not shown) give control, BIT, and indications for the system. The right card gives primary control when the airplane gets power and the left gives backup control. When the airplane changes from air to ground, the card that is in control changes. Two equipment cooling controllers (ECC) (not shown) control the supply fans and the override valve.
The low flow sensors supply both flow and temperature information.
The converter supplemental cooling check valve is part of the equipment cooling system. The converter supplemental cooling fan is part of the electrical system. See the AC generation section for more information on the converter (SECTION 24-20).
The smoke detector is part of the fire protection system. See the electrical and electronic cooling smoke detection section for more information about the equipment cooling smoke detector (SECTION 26-19).
The forward part of the equipment cooling system has two modes of operation: auto and override (OVRD).
Forward Equipment Cooling Auto Mode
One supply fan operates. The right fan is primary. The left fan gives automatic backup. The fan that operates pulls cabin air through the air filter and pushes it through the override valve.
EFFECTIVITY BEJ ALL 21-27-00
Page 12
D633W101-BEJ Sep 05/2002
A/C -EQUIPMENT COOLING -FWD SYS -GENERAL DESCRIPTION -MECHANICAL
The override valve is closed to ambient and open (NORM position) to let the cabin air from the supply fan go to these areas:
*
Forward cargo compartment -E5 and E16 racks
*
Main equipment center (MEC) -E1, E2, E3, and E4 racks
*
Forward equipment center -landscape cameras and
weather radar (WXR)
*
Flight deck -instrument, center aisle stand, and overhead panels and the maintenance access terminal (MAT).
The vent fan pulls air from these areas:
*
Main equipment center (MEC) -E1, E2, E3, and E4 racks
*
Flight deck -instrument, center aisle stand, and overhead panels and the MAT.
When electrical power is available, the vent fan operates most of the time. The fan is off for engine start. This logic helps to keep fumes from outside the aft pressurization outflow valve out of the airplane during engine start.
The air from the vent fan goes to the vent valve and the forward cargo heat valve. Only one of the valves is open at a time. When the total air temperature (TAT) goes above 55F (12.8C), the vent valve opens and the cargo heat valve closes. The air goes to the area near the forward outflow valve in the MEC. When TAT goes below 50F (10C), the forward cargo heat valve opens and the vent valve closes. The air goes to heat the forward cargo compartment.
EFFECTIVITY
BEJ ALL
Forward Equipment Cooling Override Mode
The override mode cools the equipment without the supply and vent fans. This mode uses cabin differential pressure to cause air flow through the equipment. The override mode gives sufficient cooling when the airplane is pressurized and above 25,000 feet (7625 meters). The flight crew also selects this mode when they want to clear smoke from the flight compartment.
Any of these conditions causes the system to operate in the override mode:
*
Equipment cooling switch on the air conditioning panel (not shown) set to OVRD
*
Low flow in MEC and F/D supply ducts and airspeed more than 150 knots
*
Left and right supply fans failed off
*
Smoke in supply or vent duct
*
Forward cargo fire extinguishing system armed.
The override mode causes these effects:
*
The bulk cargo ventilation fan goes off (only with equipment cooling switch in the OVRD position)
*
Both supply fans stop
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