21-52-00
ALL ú ú 03 Page 11 ú Mar 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
(b)
(c)
A
737-300/400/500MAINTENANCE MANUAL
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 controller 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 controller which positions the ram air 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.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.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
21-52-00
ALL ú ú 03 Page 12 ú Mar 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
RAM AIR SYSTEM - TROUBLE SHOOTING
_________________________________
1. General_______
A. If a system trips off from overheat but without excess air supply, the ram air system should be suspected. Make sure that the ram air inlet and exhaust doors are open. If unwanted material such as paper or cloth are ingested into the ram air system, they could restrict air flow through the system. Inspection doors are provided in the ram air ducts forward of each heat exchanger for duct inspection. If difficulty occurred during flight while flaps were in any position other than fully retracted, do a check of the cooling system (AMM 21-51-00/501). If the system has tripped off without excessive temperature being recorded, the thermal switches may be defective and should be checked.
B. It is recommended that you review AMM 20-10-27/201 before you use heating equipment on system components.
2. Equipment and Materials_______________________
A. Tempcal Multirange Thermocouple and Thermal Switch Tester - H294 with BH 17336 probe.
3. Trouble Shooting________________
A. Trouble shooting is provided for these faults:
(1)
RAM DOOR FULL OPEN light(s) will not come on when the airplane is on the ground (Figure 101).
(2)
Ram air door stays open in cruise (RAM DOOR FULL OPEN light(s) stays on continuously)(Figure 102).
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù.
BEJ 061, 062, WITHOUT SB 21-1102 ú 21-52-00
ú CONFIG ú 10 Page 101 ú Jul 15/95
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
NOTE:This procedure does troubleshooting of the components for the left ram air system. The data in the parentheses (component numbers, connector numbers, pin numbers) is for the troubleshooting of the right ram air system.
