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When the switch is in the HIGH position, solenoid B is
deenergized. When solenoid B is deenergized, the FCSOV is
in the high flow mode.
Solenoid A is energized when the all of these conditions are
true:
* The pack switch is in the HIGH position
* The APU bleed switch is in the ON position
* The APU operates above 95%
* The airplane is on the ground.
When solenoid A is energized the FCSOV operates in the APU
high flow mode.
AIR CONDITIONING - COOLING - FLOW CONTROL AND SHUTOFF VALVE - ELECTRICAL FUNCTIONAL DESCRIPTION
EFFECTIVITY
GUN 001-099, 201-999 21-50-00
Page 86
D633A101-GUN Oct 10/2005
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
21-50-00-811
AIR CONDITIONING - COOLING - FLOW CONTROL AND SHUTOFF VALVE - ELECTRICAL FUNCTIONAL DESCRIPTION
AIR CONDITIONING - COOLING - FLOW CONTROL AND SHUTOFF VALVE - ELECTRICAL FUNCTIONAL DESCRIPTION
EFFECTIVITY
GUN 001-099, 201-999 21-50-00
Page 87
D633A101-GUN Oct 10/2005
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
21-50-00-811
Purpose
The primary heat exchanger (HX) removes heat from bleed air
going to the compressor section of the air cycle machine (ACM).
The primary plenum/diffuser lets ram air flow through the
primary heat exchanger and out the ram air exhaust.
Location
The primary heat exchanger and plenum/diffuser are in the aft,
outboard section of the air conditioning compartment.
Physical Description
The primary heat exchanger is an air-to-air, plate-fin, cross-flow
type heat exchanger. Two isolated airstreams flow through thin
walled channels. The channel walls are made up of plates and
fins that increase surface area.
The primary plenum/diffuser has an outer duct and an inner
duct. The outer duct is the plenum and the inner duct is the
diffuser. The inner duct has a fan bypass check valve. The fan
bypass check valve is a hinged door assembly in the lower aft
section of the diffuser.
Functional Description
Air from the FCSOV flows through the primary heat exchanger.
A cross flow of ram air removes heat before the air enters the
ACM compressor inlet.
When the airplane is on the ground, the ACM impeller fan
makes a low pressure zone. This pulls air through the heat
exchangers and up through the plenum to the impeller fan.
Then the impeller fan sends the air through the diffuser and out
the ram air exhaust. The air pressure in the diffuser keeps the
check valve closed.
When the airplane is in flight, ram air pressure opens the fan
bypass check valve.
Training Information Point
The primary heat exchanger efficiency decreases as dirt and
contamination collect on the cooling surfaces. A RAM DOOR
FULL OPEN light that stays on in flight can be an indication of a
dirty heat exchanger.
The primary heat exchanger plenum has an access panel for
inspection and clean out.
AIR CONDITIONING - COOLING - PRIMARY HEAT EXCHANGER AND PLENUM/DIFFUSER ASSEMBLY
EFFECTIVITY
GUN 001-099, 201-999 21-50-00
Page 88
D633A101-GUN Oct 10/2005
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
21-50-00-812
AIR CONDITIONING - COOLING - PRIMARY HEAT EXCHANGER AND PLENUM/DIFFUSER ASSEMBLY
AIR CONDITIONING - COOLING - PRIMARY HEAT EXCHANGER AND PLENUM/DIFFUSER ASSEMBLY
EFFECTIVITY
GUN 001-099, 201-999 21-50-00
Page 89
D633A101-GUN Oct 10/2005
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
21-50-00-812
Purpose
The ram air inlet ducts let cooling air flow from the ram air inlet
to the heat exchangers. The ram air exhaust ducts let air flow
from the heat exchangers discharge overboard.
Location
The ram air inlet ducts are outboard of the air conditioning
compartment. They extend forward to the ram air inlet in the
wing-to-body fairing.
The ram air exhaust ducts are aft of the air conditioning
compartments. You get access to the exhaust ducts from the air
conditioning compartment.
Physical Description
There are two ram air inlet ducts, forward and aft. The forward
duct is made of fiberglass reinforced polymer, the aft duct is
made of kevlar. The forward section of the inlet ducts attach to
the airplane structure at the forward part of the ram air inlet.
They attach to the aft section with a flex duct and band clamps.
There are tie-rods that attach the ducts to the structure at the
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