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MAINTENANCE MANUAL
SEE E SEE B
SEE A
SEE F
FWD
FWD
SEE C
SEE D
COMPRESSOR OUTLET OVERHEAT SWITCH
COMPRESSOR OUTLET SENSOR ALTITUDE SWITCH
A
B C
CABIN AIR SUPPLY CHECK VALVE PACK OVERHEAT SWITCH PACK TEMPERATURE SENSOR
D E F
Cooling Pack Components
Figure 11
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MAINTENANCE MANUAL
(2)
The altitude switch is a pressure sensing aneroid with a single-pull double-throw electrical switch. A bleed port lets air enter the altitude switch housing assembly. As the pressure in the housing assembly decreases, the aneroid expands and pushes against the electrical switch. At an altitude of 31,000 feet, the aneroid closes the electrical switch.
(3)
When the altitude switch closes, the automatic-pack-temperature controller changes the limit of the air cooling pack temperature from 35°F (1.7°C) to 0°F (-18°C). At low altitude the 35°F (1.7°C) temperature limit is used to prevent ice at the condenser and the water extractor.
P.
Compressor Outlet Temperature Sensor (Fig. 11)
____________________________________
(1)
For each air cooling pack, two compressor-outlet-temperature sensors supply a resisitive signal of the temperature at their position. One sensor sends a signal to the automatic-pack-temperature controller. The other sensor sends a signal to the standby-pack-temperature controller. The sensors are installed adjacent to each other, at the air-cycle-machine-compressor outlet.
(2)
Each sensor has a platinum element which is hermetically sealed in a stainless probe. The electrical resistance of the platinum element changes as a direct and linear function of the temperature. The automatic-pack-temperature controller uses the signal to control the position of the temperature control valve. The standby pack temperature controller uses the signal to position the low-limit-control valve. The position of these two valves controls the compressor outlet temperature.
Q.
Compressor Outlet Overheat Switch (Fig. 11)
_________________________________
(1)
In each air cooling pack, a compressor-outlet-overheat switch is installed at the air-cycle-machine-compressor outlet. The switch is a thermal protective device. When it closes, it sends a signal to the flow control card that an overheat condition has occurred. The switch closes when the temperature is greater than 490°F (254°C). The switch opens again when the temperature is less than 450°F (232°C).
R.
Pack Outlet Overheat Switch (Fig. 11)
___________________________
(1) The pack-outlet-overheat switch is at the condenser outlet. The switch is a thermal protective device. When the pack outlet becomes too hot, the switch sends a signal to the flow control card. The switch closes when the temperature is greater than 190°F (88°C). The switch opens again when the temperature is less than 160°F (71°C).
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(2) The pack-outlet-overheat switch has a temperature-sensitive element with a bimetallic, snap-acting disc. As the temperature of the element increases, the metals of the disc are expanded. At a specified temperature, the disc moves suddenly to its opposite shape. This causes the switch to close.
S. Cabin Air Supply Check Valve (Fig. 11)____________________________
(1)
The cabin-air-supply-check valve prevents the flow of air from the mix manifold into the air cooling packs. The check valve has a spring, a flapper plate, and a stop. The top of the flapper plate is attached by a horizontal hinge to the inside of the check valve. The spring is installed on the hinge to push against the flapper plate. A stop is installed on the top of the check valve to limit how far the flapper can move.
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