(2)
The wing and lower aft body overheat detection system is divided into left and right sections. The right overheat section consists of sensing elements connected in series with the right temperature control unit and overheat test relay K1 to form a closed circuit sensing loop. The left overheat section consists of sensing elements connected in series through three test switches to the left and APU overheat temperature unit to form a closed circuit sensing loop. Test switches on the compartment overheat accessory unit enable a malfunction in the left overheat section to be isolated.
(3)
The overheat detection system can be tested by an overheat test switch on the air conditioning module. The overheat test switch tests continuity through the sensing loops by simulating an overheat condition. If the left detection system fails to test, the area of the malfunction can be isolated by operating the switches on the compartment overheat accessory unit.
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26-18-00
ALL ú ú 01 Page 1 ú Jul 12/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
(4) The right sensing loop elements are at engine 2 strut cavity, right wing bleed air duct, right wing leading edge, and right air conditioning packs. The left sensing loop elements are at engine 1 strut cavity, left wing bleed air duct, left wing leading edge, left air conditioning packs, keel beam, aft cargo compartment, and APU cavity.
C. AIRPLANES WITH ELECTRONIC FENWAL M237 COMPARTMENT OVERHEAT ACCESSORY UNIT; Refer to the data that follows:
(1)
The wing and lower aft body overheat detection system consists of an overheat test switch and overheat lights on air conditioning module P5-10, compartment overheat accessory unit, master caution lights, and sensing elements. The sensing elements are connected to the compartment overheat accessory unit. The accessory unit contains a control card which has a microprocessor and a relay board which monitor the resistance of the sensing elements. When a temperature rise causes the resistance to drop to a value corresponding to the alarm temperature, the compartment overheat accessory unit will provide a signal to the applicable warning light and the master caution light control section in the air conditioning module. When a alarm/fault condition is found the condition is stored in the non-volatile memory of the Fenwal compartment overheat accessory unit, the MAINT ADV light will illuminate when a condition is stored in memory. The MAINT ADV light will not extinguish until the condition is corrected and the memory is cleared.
(2)
The wing and lower aft body overheat detection system is divided into left and right sections. The right overheat section consists of a single detector loop with sensing elements connected in series. The left overheat section consists of four separate detector loops with sensing elements connected in series. All five loops are monitored by the control card in the compartment overheat accessory unit. The compartment overheat accessory unit can isolate an alarm/fault condition to each of the five loops, which can be displayed as a code on the LED display. The codes, as defined on the compartment overheat accessory unit cover plate, isolate the condition to the specific location and condition; an alarm, an open loop fault, or a short circuit loop fault. A list of the fault codes can be found in AMM 26-18-00/101 and AMM 26-18-11/501.
(3)
The right sensing loop elements are at engine 2 strut cavity, right wing bleed air duct, right wing leading edge, and right air conditioning packs. The left sensing loop elements are at engine 1 strut cavity, left wing bleed air duct, left wing leading edge, left air conditioning packs, keel beam, aft cargo compartment, and APU cavity.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
26-18-00
ALL ú ú 01 Page 2 ú Jul 12/00
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
(4) The wing and lower aft body overheat detection system can be tested by an overheat test switch on the air conditioning module. The overheat test switch tests continuity through the sensing loops by simulating an overheat condition.
NOTE: With the Fenwal compartment overheat accessory unit, the
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