M348 AFT CARGOM1147 AFT CARGOM347 AFT CARGOM275 AFT OVHT
ECS DUCT LEAK AND W/W FIRE DETECTION CONTROL CARD
COMPTCOMPTCOMPTDET SEC 56 PANEL P5-10 AIR CONDITIONING OVHT DET OVHT DET OVHT DET
M237 COMPARTMENT OVERHEAT ACCESSORY UNIT (E3-2)
Wing and Lower Aft Body Overheat Detection System Simplified Schematic
Figure 2 (Sheet 2)
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26-18-00
COMPARTMENT OVERHEAT ACCESSORY UNIT ú ú 02 Page 7 ú Nov 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
C. Overheat Light
(1) The overheat light is controlled by the left and APU temperature control unit. An overheat or a simulated overheat condition in the left overheat section will energize the output relay of the left and APU overheat control unit and provide a signal for the steady illumination of the light. The light has a press-to-test feature. The test light will also illuminate whenever the left overheat light on the air conditioning module illuminates.
D. Test Switches
(1)
Three switches in the left sensing loop facilitate isolating and locating a malfunction. Each switch has three positions and is spring-loaded to center position.
(2)
The test switches are in series with the sensing elements. Each test switch may be actuated in turn to determine which section of the detection system has malfunctioned. When a test switch is pushed up, the applicable part of the detector circuit is tested for a ground fault (fault alarm). The overheat light will illuminate if a sensor circuit is grounded. The overheat light will remain off if the sensor circuit is broken. Pushing a test switch down checks the applicable part of the detector circuit for continuity.
(3)
Test switch No. 1 tests the detector circuit from the control unit through the left wing sensing elements to the test switch. Test switch No. 2 tests the detector circuit from test switch No. 1 through the air conditioning pack sensing elements to test switch No. 2. Test switch No. 3 tests the detector circuit from test switch No. 2 through the forward and aft keel beam sensing elements to test switch No. 3.
E. Overheat Test Relay
(1) The overheat test relay is energized by pressing the overheat test switch. When energized, the relay grounds the sensing loops.
4. AIRPLANES WITH FENWAL M237 COMPARTMENT OVERHEAT ACCESSORY UNIT; Compartment Overheat Accessory Unit Components (Fig. 2)______________________________________________
A. The compartment overheat accessory unit is on electronic equipment rack E3 in the electronic compartment.
B. The cover plate of the M237 compartment overheat accessory unit contains an LED display, a MAINT ADV light, and four BITE pushbutton controls as follows:
(1)
MEM READ - Accesses the non-volatile memory.
(2)
MEM CLEAR - Clears the non-volatile memory.
(3)
LOC TEST - Initiates self-test of the control circuits and sensing elements.
(4)
DISP TEST - Initiates self-test of the control circuits and the LED display.
5. Master Caution and Annunciator Lights_____________________________________
A. The master caution and annunciator lights are on the lightshield module P7. When overheat occurs, the master caution and annunciator lights illuminate.
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26-18-00
ALL ú ú 02 Page 8 ú Nov 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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