21-52-00
 ALL  ú ú 02 Page 9 ú Mar 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 (3)  
AIRPLANES WITHOUT RAM AIR EXHAUST LOUVERS (POST-SB 21-1123); Ground Operation

 (a)  When the airplane is on the ground the landing gear safety relay and the air-ground relay complete a circuit to the open side of the actuator and open all circuits to the close side. If the modulation panel is not already full open, it will drive full open and the actuator position switches will move to the positions shown in Fig. 2. The deflector is mechanically linked to the inlet modulation panel and will be fully extended at this time. At the same time another position switch (switch 3) in the actuator completes a circuit for the RAM DOOR FULL OPEN light.

 (4)  
AIRPLANES WITH RAM AIR EXHAUST LOUVERS (PRE-SB 21-1123); Flight Operation

 (a)  When the airplane breaks ground on takeoff the air-ground relay becomes de-energized but the turbofan control relay stays energized because the flaps are down. This completes a circuit to the close side of the actuator through another position switch (switch 2) and the actuator moves to position 2. At actuator position 2 the inlet modulation panel and exhaust louvers have moved to a slightly closed position, but not one which will appreciably affect ram airflow (Fig. 2). At this position, however, the deflector door will have moved to the faired position. Any additional movement of the inlet panel will not affect the position of the deflector because the mechanism is against its stop. A cam link and torsion spring permits further movement of the panel.
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 21-52-00
 ALL  ú ú 03 Page 10 ú Mar 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 (b)  
After takeoff, when the flaps are fully retracted, the turbofan control relay becomes de-energized, the turbofan valve drives closed, and a circuit is completed to the ram air controller. This circuit continues to drive the actuator toward close until actuator position 3 is reached. At position 3 the actuator position switch (switch 3) closes. From this point on, as long as the flaps are up the ram air control will position the actuator somewhere between position 3 and 4. The positioning of the actuator depends on the temperature of the air at the air cycle machine compressor discharge. A temperature sensor, located in the air cycle machine compressor discharge duct, provides a signal to the ram air control which positions the ram air exhaust louvers and inlet modulation panel. The ram air controller sends either an extend or retract signal to the ram air actuator which controls air flow through the ram air ducts and holds air cycle machine compressor discharge temperature to as near 230°F as possible. On cold days it may not be possible to attain the 230°F temperature. If this be the case, the actuator will drive to position 4, (full extend) and remain there until the temperature rises or flaps are lowered for landing. During approach and landing the ram air modulation system reverses the sequence noted for on-the-ground and takeoff conditions.

 (c)  
On hot days or if the heat exchanger is operating at marginal efficiency, it may not be possible to cool the air cycle machine compressor discharge temperature to 230°F. If this is the case, the actuator will drive to position 1 (actuator full retract) and will remain there until the temperature cools below 230°F. The RAM DOOR FULL OPEN light will be on under these conditions.

 (5)  AIRPLANES WITHOUT RAM AIR EXHAUST LOUVERS (POST-SB 21-1123); Flight Operation
 (a)  When the airplane breaks ground on takeoff the air-ground relay becomes de-energized but the turbofan control relay stays energized because the flaps are down. This completes a circuit to the close side of the actuator through another position switch (switch 2) and the actuator moves to position 2. At actuator position 2 the inlet modulation panel has moved to a slightly closed position, but not one which will appreciably affect ram airflow (Fig. 2). At this position, however, the deflector door will have moved to the faired position. Any additional movement of the inlet panel will not affect the position of the deflector because the mechanism is against its stop. A cam link and torsion spring permits further movement of the panel.
　
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