(d)
When an alarm/fault condition is identified, the code is stored in the non-volatile memory for recall as required. The condition is stored in non-volatile memory until the condition is resolved and the memory is cleared. The fault history stores the last ten codes that were cleared from the active non-volatile memory. Access to these functions is gained through the four BITE pushbutton switches on the M237 module cover plate (AMM 26-18-00 201).
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
WING AND LOWER AFT BODY OVERHEAT DETECTION SYSTEM -
___________________________________________________ TROUBLE SHOOTING
________________
1. General_______
A. Two wing and lower aft body overheat detection system troubles are false alarm and no alarm. Test switches isolate most troubles. The system test switch is on air conditioning module P5-10. Pressing switch causes overheat lights on module to illuminate. If the left or right overheat warning lights do not illuminate, there is either an open circuit in the sensing loop or the sensor loop resistance exceeds the alarm threshold of the M237 Compartment Overheat Accessory Unit. The Fenwal M237 unit has an alarm threshold of 115 ohms. The Boeing M237 unit has an alarm threshold between 25 and 50 ohms. Because of this, when you check the resistance of the sensor loops, you check for a different resistance if the Fenwal unit is installed than if the Boeing unit is installed. The higher the alarm threshold, the higher the resistance for which you check. If the right overheat light fails to illuminate, right strut cavity sensor, right wing sensor, right air conditioning pack sensor or right control unit in compartment overheat accessory unit may be faulty. Trouble shoot per right overheat system trouble shooting chart. If left overheat light on module fails to illuminate, left overheat sensors may be tested and isolated by toggle switches on compartment overheat accessory unit. The toggle switches provide continuity and ground fault checks of each sensor.
B. A false alarm usually is due to a short to ground in power wire of a heat sensing loop. If trouble shooting isolates trouble to heat sensing loop or airplane wiring, check for improperly installed electrical connectors, moisture may have entered at an improper connection. Remove moisture by blowing out connectors with dry nitrogen.
C. Prior to tests, install equivalent test connectors (wire end fittings) at receptacle. Test connector has exposed contact points or wires to attach to or touch test probes. Test connector protects airplane wire from possibility of arcing or other damage and provides position contact for attachment of test equipment.
D. ON AIRPLANES WITH FENWAL M237 OVERHEAT CONTROL UNITS, these fault codes will be displayed on the M237 unit front panel:
ZONE/SITUATION ALARM (2) OPEN LOOP SHORT LOOP
LEFT WING LE 14 12 10 LEFT AC PACK BAY 24 22 20 KEELBEAM 34 32 30 AFT CARGO SECT 44 42 40 RIGHT WING LE AND AC PACK BAY 64 62 60 WHEEL WELL FIRE 84 --
IN PROGRESS NOT COMPLETE COMPLETE
LOCAL TEST 90 98 99
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
2. Prepare for Trouble Shooting
____________________________
A. Procedure
(1)
Provide electrical power (AMM 24-22-00/201).
(2)
Check that OVHT WHL WELL WNG BDY and MASTER WARN & CONTROL circuit breakers on panel P6-2 are closed. Check that MASTER CAUTION ANNUNCIATOR NO. 1, MASTER CAUTION ANNUNCIATOR BAT, MASTER CAUTION AIR COND, DIM & TEST, and nine INDICATOR MASTER DIM BUS circuit breakers on panel P6-3 are closed.
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