B737 Bleed Air Control Panel

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.
  • 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.

Engine BLEED Air Switch

  • OFF: Closes engine Pressure Regulating Shutoff Valve (PRSOV).
  • 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.
    • Lights remain illuminated until reset.