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A 737-300/400/500MAINTENANCE MANUAL
Conditioned Air Temperature Control Systems - Component Location
Figure 1 (Sheet 3)
G95323
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A
737-300/400/500MAINTENANCE MANUAL
SEE A
VALVE POSITION TRANSMITTER
TO AIR CYCLE MACHINE
TO MIXING CHAMBER
FWD INBD VISUAL POSITION INDICATOR
SEE B
COLD VALVE
VALVE ACTUATOR
A
HOT VALVE VALVE POSITION INDICATOR
HOT
COLD
B
Air Mix Valve Figure 2
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A
737-300/400/500MAINTENANCE MANUAL
G. The manual temperature regulating components consists of two switches, in the temperature selector assembly, which are electrically connected to the mix valve actuator. The automatic temperature regulating components include a temperature selector assembly, a controller, cabin temperature sensor, anticipator sensor, and a duct temperature limiting sensor.
2. Air Mix Valve_____________
A. The mix valve consists of two butterfly valves operated by the same actuator through a common shaft. The 115 volt ac actuator mounts on a flange of the hot valve to drive the common shaft. When the hot valve butterfly is full open the cold valve is full closed and vice versa. As the hot valve moves toward close, the cold valve moves proportionally toward open. A position potentiometer is connected to the opposite end of the shaft from the actuator to permit monitoring the valve position from the control cabin. A visual indicator is also located at the actuator between the potentiometer and the cold valve body (Fig. 2).
B. Limit switches in the actuator housing interrupt current to the actuator monitor at either extremity of travel. The mix valve is located in the air conditioning equipment bay inboard of the heat exchangers.
3. Thermal Sensing Units_____________________
A. Thermal sensing units in the temperature control system consist of thermal switches, temperature bulbs, and temperature sensors. Thermal switches are used to protect against duct overheat, temperature bulbs are used in conjunction with indicators for monitoring passenger cabin temperature and passenger cabin supply duct temperature, and temperature sensors are used with the automatic temperature regulation systems to automatically position the mix valves in obtaining selected temperatures for the cabins.
B. The thermal switches consist essentially of a bimetal element enclosed in a steel probe. The thermal switch contacts are normally open. At a predetermined temperature the contacts will close. A 190°F ((88°C) passenger cabin duct overheat thermal switch and a 250°F (121°C) passenger cabin duct overheat thermal switch are used in each control system. The switches are mounted in the main distribution manifold and in the overhead distribution manifold adjacent to its union with the RH riser duct (Fig. 1).
C. Temperature bulbs consist of a temperature sensitive resistance element within a tube. As the temperature of the element changes, its resistance changes accordingly to cause movement of an indicator pointer.
(1)
The passenger cabin temperature bulb is installed with the passenger cabin temperature sensor inside a duct located below the stowage compartment (Detail A, Fig. 1). An in-line fan downstream of the bulb and sensor draws air from the cabin across the bulb and sensor.
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