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.
Objective: To prevent possible backpressure of the APU.
ISOLATION VALVE Switch
OPEN: Opens isolation valve.
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.
WING – BODY OVERHEAT Light
Illuminated (amber):
Left light indicates overheat from bleed air duct leak in the 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 the right engine strut, right inboard wing leading edge, or right air conditioning bay.
ON: Opens engine Pressure Regulating Shutoff Valve (PRSOV) 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.
Illuminates both MASTER CAUTION lights.
Illuminates AIR COND light.
BLEED Light
Illuminated (amber):
Excessive engine bleed air temperature, over-pressure, or under-pressure – Related engine PRSOV closes automatically and requires reset. OR
A failure within the bleed air system – Bleed system failure may not be resettable. OR
An incorrect bleed air configuration after takeoff or go-around – Turning either BLEED switch ON will extinguish both BLEED lights if lights illuminated because of a configuration problem.
TRIP RESET Switch
Push (if fault condition is corrected):
Resets BLEED, PACK, or ZONE TEMP lights.
Related engine bleed valve opens, or related pack valve opens, or related trim air modulating valve opens.
