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uses the air (temperature) sensor signal in a bridge circuit. The
bridge circuit reads the ACM compressor temperature as an
error signal, too hot or too cold. The nominal (balanced) control
temperature is 230F/110C. The output sends a retract (too hot)
signal through S3 or a (too cold) signal to extend the actuator
through S4. The switch positions S3 and S4 in the actuator are
the control limits for cruise mode.
If the pack is shut down in flight, the ram air modulation panels
fairs (closes) to decrease drag.
Training Information Point
If the DOOR FULL OPEN LIGHT is on during flight cruise mode,
it may be one of these three possible problems:
* The ram air system may have a blockage
* The heat exchangers are dirty
* Electrical failure.
AIR CONDITIONING - COOLING - RAM AIR SYSTEM - FUNCTIONAL DESCRIPTION
EFFECTIVITY
GUN 101-118 21-50-00
Page 34
D633A101-GUN Oct 10/2006
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
21-50-00-028
AIR CONDITIONING - COOLING - RAM AIR SYSTEM - FUNCTIONAL DESCRIPTION
AIR CONDITIONING - COOLING - RAM AIR SYSTEM - FUNCTIONAL DESCRIPTION
EFFECTIVITY
GUN 101-118 21-50-00
Page 35
D633A101-GUN Oct 10/2006
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
21-50-00-028
Purpose
The air cycle machine (ACM) decreases air temperature, by
expansion through a turbine.
Location
The air cycle machine is in the air conditioning compartment.
There is an ACM for each of the left and right pack systems.
Physical Description
The air cycle machine is a high-speed rotating assembly. It has
these three sections connected by a common shaft:
* Turbine
* Compressor
* Impeller Fan.
Foil air bearings support the shaft. The air bearings let the ACM
turn at high speed with little friction.
Training Information Point
You can cause damage to the air bearings if the shaft turns in
the wrong direction.
It is not necessary to do servicing of air cycle machines that
have air bearings.
The ACM is part of the secondary pack assembly. It has two
clevis brackets for attachment to the structure in the air
conditioning compartment.
AIR CONDITIONING - COOLING - AIR CYCLE MACHINE
EFFECTIVITY
GUN 101-118 21-50-00
Page 36
D633A101-GUN Oct 10/2006
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
21-50-00-022
AIR CONDITIONING - COOLING - AIR CYCLE MACHINE
AIR CONDITIONING - COOLING - AIR CYCLE MACHINE
EFFECTIVITY
GUN 101-118 21-50-00
Page 37
D633A101-GUN Oct 10/2006
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
21-50-00-022
Purpose
The secondary heat exchanger (HX) removes heat from bleed
air that comes from the compressor section of the air cycle
machine (ACM).
The secondary plenum/diffuser permits ram air to flow through
the secondary heat exchanger and out the ram air exhaust.
Location
The secondary heat exchanger and plenum/diffuser assembly
is forward of the primary heat exchanger and plenum/diffuser
assembly.
Physical Description
The secondary heat exchanger is an air-to-air, plate-fin,
counter-flow type. Two isolated airstreams flow through thin
walled channels. The channel walls are made up of plates and
fins that increase surface area.
The secondary plenum/diffuser has an outer duct and an inner
duct. The outer duct is the plenum and the inner duct is the
diffuser.
Functional Description
Air from the ACM compressor outlet flows through the
secondary heat exchanger. A cross flow of ram air removes
heat before the air enters the ACM turbine 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.
When the airplane is in flight, the ram air pressure flows down
the plenum and out the fan bypass check valve.
Training Information Point
The secondary heat exchanger efficiency decreases as dirt and
contamination collect on the cooling surfaces.
The secondary heat exchanger plenum has a access panel for
inspection and clean out.
AIR CONDITIONING - COOLING - SECONDARY HEAT EXCHANGER AND PLENUM/DIFFUSER ASSEMBLY
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