26-17-00
 ALL  ú ú 02 Page 6 ú Nov 15/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

28V DC
BATT BUS MASTER WARNING AND CONTROL
115V AC TRANSFER BUS 1
WHEEL WELL
WING AND
LOWER BODY OVHT

P6 PANEL
FIRE WARN LIGHTS & BELL CUTOUT
CUTOUT CAPT P7 LIGHTSHIELD
BELL
AURAL WARN
BOX (M315)

BELL CUTOUT CUTOUT F/O
WHEEL WELL WHEEL WELL WARNING LIGHT
TEST FAULT INOP
SWITCH FIRE OVHT
P8-1 ENGINE AND APU FIRE CONTROL MODULE
737-300/400/500
MAINTENANCE MANUAL

A4 TEMPERATURE CONTROL UNIT
Q1
Q2
A5 COMPARTMENT OVERHEAT UNIT
K2
M237 COMPARTMENT OVERHEAT ACCESSORY UNIT (E3-2)
K1
T3
T2
ALARM
T1
STBY
WHEEL WELL OVERHEAT DETECTOR ELEMENT
T78859
Wheel Well Overheat Detection System Simplified Schematic
Figure 2 (Sheet 1)

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH BOEING M237 ú

 26-17-00
 COMPARTMENT OVERHEAT ACCESSORY UNIT  ú ú 02 Page 7 ú Nov 15/91
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL

WHEEL WELL
OVERHEAT DETECTOR
ELEMENT

Wheel Well Overheat Detection System Simplified Schematic Figure 2 (Sheet 2)
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH FENWAL M237 ú

 26-17-00
 COMPARTMENT OVERHEAT ACCESSORY UNIT  ú ú 02 Page 8 ú Nov 15/92
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 WHEEL WELL OVERHEAT DETECTION SYSTEM - TROUBLE SHOOTING
_______________________________________________________
 1.  General_______
 A.  Two wheel well fire detection system troubles are false alarm and no alarm. If wheel well warning light, master fire warning lights, or alarm bell do not operate, the trouble is in the associated circuits, which should be checked before preceeding to trouble charts. A frequent trouble is flexible lead power wire or sensing element breakage.
 B.  Use AMM 26-17-00, A/T to assist in trouble shooting.
 C.  A false alarm is usually due to a short to ground in the power wire of a sensing loop. If trouble shooting per the chart isolates the trouble to the heat sensing loop, test the insulation resistance of the sensing loop. If the resistance of the sensing element is okay, but a loose or improperly connected electrical connection was noted during the test, moisture may have entered at the connection. Remove moisture by blowing out connectors with dry nitrogen.
 D.  Prior to trouble shooting, install equivalent test connectors (wire end fittings) at the receptacle. The test connector should have exposed contact points or wires to attach to or touch test probes. The test connector protects airplane wire from arcing or other damage and provides position contact for attachment of test equipment.
 E.  Whenever the engine and APU fire control panel (P8-1) is removed and replaced, test the wheel well overheat detection system (AMM 26-17-00, A/T).
 2.  Prepare for Trouble Shooting____________________________
 A.  Provide electrical power (AMM 24-22-00, MP).
 B.  Check that FIRE PROTECTION DETECTION OVHT WHL WELL WNG BDY, AURAL WARN, and MASTER WARN & CONTROL circuit breakers on panel P6-2 are closed.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 26-17-00
 ALL  ú ú 01 Page 101 ú Jun 25/84
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL

Wheel Well Overheat Detection System Troubleshooting Chart (False Alarm) Figure 101
　
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