Water Separator 35`F Control System Circuit
Figure 5
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A 737-300/400/500MAINTENANCE MANUAL
TO MAIN
DISTRIBUTION
MANIFOLD
RAM AIR DEFLECTOR DOOR
RAM AIR INLET MODULATION PANEL
RAM AIR
INLET
210` F
THERMAL SW
WATER SPRAY
INJECTOR
390` F
THERMAL SW
SECONDARY
HEAT
EXCHANGER
PRIMARY
HEAT
EXCHANGER
Right Air Cycle System Airflow Diagram
(Left Air Cycle System Similar)
Figure 6
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A
737-300/400/500MAINTENANCE MANUAL
D. The 35°F sensor is one element of the 35°F control. The control contains a bridge circuit, an amplifier, and a silicon-controlled rectifier actuator control. The sensor is utilized as a remotely located variable resistance for one leg of the bridge circuit. As temperature at the sensor changes, its resistance changes, unbalancing the bridge. The bridge circuit is connected to the amplifier. The amplifier interprets the signal received and then signals the actuator control to move the valve open or closed. When the bridge is balanced current is shut off to the valve and it maintains the position held. The bridge balances with temperature in the separator at approximately 35°F.
E. The 35°F controls have built-in test circuits which provide a quick check of the 35°F control system. A test switch, two indicator lights and a test instruction placard have been added to these units. The test switch is a rotary type with five test positions and one flight position. When control system is not being tested, the switch must be returned to the flight position.
11. Operation_________
A. When air conditioning is turned on, the pack valves open and hot air from the pneumatic system enters the air conditioning system. Depending on cabin temperature requirements, the mix valves adjust to send the required portion of this air through the air cycle system. The remainder passes unchanged through a duct to the mixing chamber (Fig. 6).
B. The air entering the system first passes through the primary heat exchanger where heat is removed. This air, still at an elevated temperature, moves on to the air cycle machine where it passes through the compressor and the secondary heat exchanger before it reaches the turbine. At this point, some air is diverted to the ram air water spray injector to aspirate the water separator water. The turbine then drives the compressor. As the air is compressed, its temperature and pressure rise. The secondary heat exchanger then lowers the temperature. The air expands as it drives the turbine and leaves the turbine at the coolest temperature of the cycle.
C. Should the temperature of the air leaving the compressor reach 390 |10°F, the compressor discharge overheat switch will close to energize the pack overheat relay. Energizing the relay completes circuits to close the pack valve, illuminate the PACK TRIP OFF and AIR COND master caution annunciators. Pushing the TRIP RESET switch will return the system to normal operation after the overheat condition has been corrected.
D. Unless the secondary heat exchanger reduces the temperature of the air sufficiently, overheat of the turbine may occur. At a turbine inlet temperature of 210 |10°F (93 to 104°C), the turbine inlet overheat switch will close. Closing of this switch will also energize the pack trip relay to close the pack valve, illuminate the PACK TRIP OFF light and AIR COND master caution annunciators. Pushing the TRIP RESET switch will return the system to normal operation after the overheat conditon has been corrected.
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