Air Systems -Air Conditioning System Description
737 Flight Crew Operations Manual
Standby Pack Average Temperature
If all zone controls and primary pack controls fail, the standby pack controls command the packs to produce air temperatures which will satisfy the average temperature demand of the two cabin zones. The trim air modulating valves will close. The flight deck zone Temperature Selector will have no effect on the standby pack controls.
Fixed Cabin Temperature
If all Temperature Selectors are positioned OFF, the pack controls will cause the left pack to maintain a fixed temperature of 75°F (24°C) and the right pack to maintain 65°F (18°C) as measured at the pack temperature sensor.
Air Conditioning Distribution
Conditioned air is collected in the mix manifold. The temperature of the air is directly related to the setting of the Temperature Selectors.
Overheat detection is provided by temperature sensors located downstream of the packs and the mix manifold. An overheat condition causes the appropriate trim air modulating valve to close and the ZONE TEMP light to illuminate.
Flight Deck
Since the flight deck requires only a fraction of the air supply provided by the left
pack, most of the left pack output is routed to the mix manifold.
Conditioned air for the flight deck branches into several risers which end at the
floor, ceiling and foot level outlets. Air diffusers on the floor under each seat
deliver continuous air flow as long as the manifold is pressurized.
Overhead diffusers are located on the flight deck ceiling, above and aft of the No.
3 windows. Each of these outlets can be opened or closed as desired by turning a
slotted adjusting screw.
There is also a dual purpose valve behind the rudder pedal of each pilot. These
valves provide air for warming the pilots' feet and for defogging the inside of the
No. 1 windshields. Each valve is controlled by knobs located on the Captain's and
First Officer's panels.
Passenger Cabin
The passenger cabin air supply distribution system consists of the mix manifold,
sidewall risers, and an overhead distribution duct. Sidewall risers go up the right and left walls of the passenger cabin to supply air to the overhead distribution duct. The overhead distribution duct routes conditioned air to the passenger cabin. It extends from the forward to the aft end of the ceiling along the airplane centerline and also supplies the sidewall diffusers.
Copyright . The Boeing Company. See title page for details.
Air Systems -Air Conditioning System Description 737 Flight Crew Operations Manual
Recirculation Fan
The recirculation fan system reduces the air conditioning system pack load and the engine bleed air demand. Air from the passenger cabin and electrical equipment bay is drawn to the forward cargo bay where it is filtered and recirculated to the mix manifold. The fans are driven by AC motors. Each recirculation fan operates only if the respective RECIRC FAN Switch is selected to AUTO. In flight, the left recirculation fan operates if both packs are operating unless either PACK switch is in HIGH. The right recirculation fan operates in flight if both packs are operating unless both PACK switches are in HIGH. On the ground, the left recirculation fan operates unless both PACK switches are in HIGH and the right recirculation fan operates even if both PACK switches are in HIGH.
Equipment Cooling
The equipment cooling system cools electronic equipment in the flight deck and the E & E bay.
The equipment cooling system consists of a supply duct and an exhaust duct. Each duct has a normal fan and an alternate fan. The supply duct supplies cool air to the flight deck displays and electronic equipment in the E & E bay. The exhaust duct collects and discards warm air from the flight deck displays, the overhead and aft electronic panels, circuit breaker panels in the flight deck, and electronic equipment in the E & E bay.
Loss of airflow due to failure of an equipment cooling fan results in illumination of the related equipment cooling OFF light. Selecting the alternate fan should restore airflow and extinguish the OFF light within approximately 5 seconds.
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