Bleed Air Controls and Indicators
PACK TRIP OFF 
OVERHEAT WING-BODY 
TRIP OFF BLEED 

DUAL BLEED Light
Illuminated (amber) – APU bleed air valve open and engine No. 1 BLEED air switch ON, or engine No. 2 BLEED air switch ON, APU bleed air valve and isolation valve open.

ISOLATION VALVE Switch
CLOSE – closes isolation valve.
AUTO –
.  closes isolation valve if both engine BLEED air switches are ON and both air conditioning PACK switches are AUTO or HIGH
.  opens isolation valve automatically if either engine BLEED air or air
conditioning PACK switch positioned OFF.

Air Systems -Controls and Indicators 737 Operations Manual

OPEN – opens isolation valve.

WING–BODY OVERHEAT Light
 Illuminated (amber) –
.  
left light indicates overheat from bleed air duct leak in left engine strut,
left inboard wing leading edge, left air conditioning bay, keel beam or
APU bleed air duct

.  
right light indicates overheat from bleed air duct leak in right engine strut, right inboard wing leading edge or right air conditioning bay.

Engine BLEED Air Switches
OFF – closes engine bleed air valve.
ON – opens engine bleed air valve when engines are operating.

APU BLEED Air Switch
OFF – closes APU bleed air valve.
ON – opens APU bleed air valve when APU is operating.

Bleed Air DUCT PRESSURE Indicator
Indicates pressure in L and R (left and right) bleed air ducts.

Wing–Body Overheat (OVHT) TEST Switch
PUSH –
.
tests wing–body overheat detector circuits

.
illuminates both WING–BODY OVERHEAT lights.

BLEED TRIP OFF Light
Illuminated (amber) – excessive engine bleed air temperature or pressure
.
related engine bleed air valve closes automatically

.
requires reset.

TRIP RESET Switch
PUSH (if fault condition is corrected) –
.  
resets BLEED TRIP OFF, PACK TRIP OFF and DUCT OVERHEAT
lights

.
lights remain illuminated until reset.

Copyright . The Boeing Company. See title page for details.
2.10.2   December 7, 2001

Air Systems -Controls and Indicators
Air Conditioning Controls and Indicators
PACK TRIP OFF 
WING-BODY OVERHEAT 
BLEED TRIP OFF 

AIR Temperature (TEMP) Source Selector
SUPPLY DUCT – selects main distribution supply duct sensor for TEMP indicator.
Copyright . The Boeing Company. See title page for details.
December 7, 2001  2.10.3
Air Systems -Controls and Indicators 737 Operations Manual

PASS CABIN – selects passenger cabin sensor for TEMP indicator.

DUCT OVERHEAT Light
Illuminated (amber) –
.
bleed air temperature in related duct exceeds limit

.
air mix valves drive full cold

.
requires reset.

Control (CONT) CABIN and Passenger (PASS) CABIN Temperature Selector
AUTO – automatic temperature controller controls passenger cabin or flight deck temperature as selected.
MANUAL – air mix valves controlled manually. Automatic temperature controller bypassed.

RAM DOOR FULL OPEN Light
Illuminated (blue) – indicates ram door in full open position.

Air Conditioning PACK Switch
OFF – pack signalled OFF.
AUTO –
.
with both packs operating, each pack regulates to low flow

.  
with one pack operating, operating pack regulates to high flow in flight
with flaps up

.  
when operating one pack from APU (both engine BLEED air switches
OFF), regulates to high flow.

HIGH –
.
pack regulates to high flow

.
provides maximum flow rate on ground with APU BLEED air switch ON.

AIR MIX VALVE Indicator
Indicates position of air mix valves:
.
controlled automatically with related temperature selector in AUTO

.
controlled manually with related temperature selector in MANUAL.

Air Temperature (TEMP) Indicator
Indicates temperature at location selected with AIR TEMP source selector.
Copyright . The Boeing Company. See title page for details.
2.10.4   December 7, 2001

Air Systems -Controls and Indicators 737 Operations Manual

Recirculation (RECIRC) FAN Switch
OFF – fan signalled OFF
　
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