(d)  
There are three different steps of ram air modulation as determined by three airplane positions. Fixed positions are obtained when the airplane is on the ground and on takeoff. During flight the openings vary according to airplane operation.

 (2)  
AIRPLANES WITH RAM AIR EXHAUST LOUVERS
 (PRE-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 and exhaust louvers are not already full open they 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.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
28V DC
28V DC

115V AC
28V DC
28V DC

RAM AIR ACTUATOR
AIRPLANES WITH "RAM MOD CONT" CIRCUIT BREAKER ON P6-4 CIRCUIT BREAKER PANEL
AIRPLANES WITHOUT "RAM MOD CONT" CIRCUIT BREAKER ON P6-4 CIRCUIT BREAKER PANEL
Ram Air Modulation System Schematic
Figure 2 (Sheet 1)

A54142
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
MODULATION DEFLECTOR RANGE RANGE

POSITION AIRPLANE  POSITION FLAP  SWITCH POSITION * RAM AIR ACTUATOR  POSITION ACTUATOR  POSITION VALVE TURBOFAN  POSITION PANEL MODULATION  POSITION DEFLECTOR 
1  2  3  4 
GROUND ON  DOWN OR UP 
 
 
 
 1  OPEN  OPEN FULL  EXTENDED 
TAKEOFF  DOWN 
 
 
 
 2 TO MOVES  OPEN STAYS  OPEN NORMAL TOWARD MOVES  RETRACTED 
TAKEOFF AFTER  UP 
 
 
 
 3 1 TO MOVES  CLOSES  OPEN 1 NORMAL MOVES TO  RETRACTED 
CRUISE  UP 
 
 
 
 1 3 AND 4 BETWEEN MODULATES  CLOSED STAYS  1 AND CLOSED NORMAL OPEN BETWEEN MODULATES  RETRACTED 
APPROACH LANDING  DOWN 
 
 
 
 3 TO MOVES  OPENS  OPEN NORMAL MOVES TO  RETRACTED 
DOWN TOUCH- DOWN 
 
 
 
 MOVES 1  OPEN STAYS  OPEN TO FULL DRIVES  EXTEND TO FULL DRIVES 

* SWITCH POSITION IS SHOWN FOR AIRPLANE ATTITUDE AFTER THE ATTITUDE HAS BEEN ATTAINED

ACTUATOR POSITION REMAINS AT 2 IF AMBIENT CONDITIONS AND/OR HARDWARE CONDITION ARE SUCH THAT REQUIRE MAXIMUM RAM COOLING. THIS PREVENTS MODULATION PANEL MOVING FARTHER TOWARD CLOSED
Ram Air Modulation System Schematic
Figure 2 (Sheet 2)

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

737-300/400/500MAINTENANCE MANUAL 
ACTUATOR RAM AIR 
1 LOUVER EXHAUST RAM AIR 
CABLE CONTROL 
STOP DEFLECTOR  FORWARD PANEL  CRANK  AFT PANEL  PANEL OPEN MODULATION CABLE CONTROL  ROLLER 
BODY SKIN 
DEFLECTOR  ROD  LINK EXTENSION SPRING  INLET SCOOP  ASSEMBLY ARM  PANEL CLOSE MODULATION 
GROUND POSITION  QUADRANT MODULATION PANEL RAM AIR INLET 
STOP DEFLECTOR 

AFTER TAKEOFF TO FLAPS UP POSITION
　
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