(2)
The passenger cabin supply duct temperature bulb is mounted in the main distribution manifold.
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D. The temperature sensors also untilize variable resistance type elements. As temperature increases their resistance decreases and vice versa. The sensors form a part of the automatic regulation system network to maintain selected temperatures in the control and passenger cabin. A duct limit temperature sensor, anticipator sensor, and cabin temperature sensor are used with each regulation system. The duct limit sensors and anticipator sensors are mounted in the main distribution manifold and in the overhead distribution manifold. The control cabin temperature sensor is located behind a screened opening in the ceiling, approximately 4 inches left of center, at station 259. The passenger cabin temperature sensor is installed in the same duct which encloses the passenger cabin temperature bulb (Ref par. 3.C.(1)).
4. Temperature Selectors
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A. The control and passenger cabin temperature selectors are identical units mounted on the forward overhead panel. The face dial is divided into an automatic and MANUAL range. Three switches inside the selector are provided to direct 115 volts ac to the mix valve. Two cams on a cam plate, fixed to the selector knob, close each switch separately as the knob is turned.
B. In MANUAL, turning the knob clockwise to COOL causes one of the cams to close a switch connected to the mix valve actuator motor, and operate the valve to increase the proportion of cold air passing through the valve. Turning the knob counterclockwise to WARM causes the cam to close a switch connected to the mix valve actuator and operate the valve to increase the proportion of warm air passing through the valve. When the knob is returned to OFF, both switches are open and the mix valve remains in the position to which it was last driven.
C. When the temperature selector knob is turned past the MANUAL range into AUTO, the second cam on the knob shaft closes a switch which directs power to the automatic temperature control circuit. The cam keeps the switch closed through the automatic range. In the AUTO range, the knob also drives a potentiometer which forms one leg of a cabin temperature control bridge circuit.
5. Temperature Controller
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A. Control and passenger cabin automatic temperature regulation is obtained from a single unit located in the electronic compartment. This unit contains all parts of each regulation system which are not required to be mounted remotely. Separate identical networks are enclosed for each cabin (Fig. 3).
(1) A built-in test circuit in the temperature controller provides a quick electrical check of temperature control system components. A rotary test switch, two sets of GO, NO GO lights and a test instruction decal are provided on the face of the controller. When the temperature control system is not being tested the switch must be returned to START position.
B. Each network contains a separate power supply, the fixed resistance legs of three different bridge circuits, a control amplifier, a silicon-controlled rectifier actuator control, and a pulse-forming network.
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Temperature Regulation Circuit
Figure 3
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A
737-300/400/500MAINTENANCE MANUAL
C. The three bridge circuits in use for automatic control are: cabin temperature control bridge, temperature control damping bridge, and duct temperature limit bridge.
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