21-52-00
 ALL  ú ú 02 Page 4 ú Mar 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 B.  AIRPLANES WITHOUT RAM AIR EXHAUST LOUVERS (POST-SB 21-1123); The ram air controller electrically controls the ram air actuator to position the inlet modulation panel during flight when flaps are up. The control unit is installed on the inboard side of the keel beam downstream of the turbofan. A temperature sensor is installed in the air cycle machine compressor discharge duct. See cooling air and ram air equipment location illustration, 21-50-00.
 7.  Turbofan________
 A.  The turbofan is a turbine powered fan located between sections of the ram air exhaust ducts. Air from the pneumatic system is directed through the turbofan case to a small two-stage turbine centrally located inside the case. A larger diameter fan is located forward of the turbine and is shaft-connected to the turbine. The turbofan normally operates only during ground air conditioning operation or in flight when the flaps are extended. Operation is controlled by a turbofan valve.
 8.  Turbofan Valve______________
 A.  The turbofan valve is a solenoid-actuated shutoff and regulating valve requiring 28 volt dc current and is spring-loaded to the closed position. A closed limit switch in the valve completes a circuit to the ram air controller when the valve is closed. A manual control rod on the solenoid permits opening or closing the valve manually. Two test ports are provided for checking valve operation under pressure. The left turbofan valve is located in the left equipment bay inboard of the turbofan. The right turbofan valve is located in the right pack cold air supply duct.
 9.  AIRPLANES PRE-SB 21-1123; Ram Air Exhaust Louvers_______________________
 A.  Louvers are installed at the ram air outlet to restrict airflow through the ram air system during flight. The louvers are installed parallel to each other and are supported at either end by a support angle. Individual arms are splined to mate with the outboard end of each louver and are linked together at the other end of the arm to obtain simultaneous movement of each. The forward arm mates with a torque shaft which extends from the arm to the ram air actuator located in the ram air duct cavity. As the actuator moves, the louvers rotate to reduce or increase the exhaust area. Since the torque shaft is connected to the crank which operates the ram air inlet modulation panel control cables, movement of the exhaust louvers and the inlet modulation panel is obtained at the same time. The exhaust louvers are the primary restriction to ram airflow while the inlet panel reduces the possibility of aerodynamic resonance in the ram air ducts.
 10. Inspection Doors________________
 A.  Two inspection doors in each ram air system permit visually checking for foreign material in the ram air ducts or heat exchangers. One inspection door is located on the bottom of the ram air duct just outboard of the secondary heat exchanger. The other door is located on the bottom of the duct outboard of the primary heat exchanger. Open the ram air duct access door to gain access to either inspection door.
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 21-52-00
 ALL  ú ú 02 Page 5 ú Mar 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 11. Operation_________
 A. Ram Air Modulation Control (Fig. 2).
 (1)  
General

 (a)  
Ram air modulation provides maximum airflow through the ram air system during ground operation. During flight, however, maximum airflow is seldom required. Ram air modulation permits a reduction in airflow at this time which, in turn, results in substantial drag reduction. The modulation system automatically adjusts airflow according to air conditioning requirements.

 (b)  
AIRPLANES WITH RAM AIR EXHAUST LOUVERS (PRE-SB 21-1123); The ram air modulation system consists of adjustable inlet and exhaust openings, a ram air actuator, a cable system with mechanical linkage to the modulation panel, exhaust louvers, and deflector, a ram air controller, a ram air temperature sensor, and the interrelated circuitry.

 (c)  
AIRPLANES WITHOUT RAM AIR EXHAUST LOUVERS (POST-SB 21-1123); The ram air modulation system consists of an adjustable inlet opening, a ram air actuator, a cable system with mechanical linkage to the modulation panel and deflector, a ram air controller, a ram air temperature sensor, and the interrelated circuitry.
　
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