TURBINE AND FAN ASSEMBLY.- The turbine and fan assembly (fig. 4-7), which is mounted in the heat exchanger upper plenum (7), is a removable component of the refrigeration package. High-pressure, partially cooled bleed air drives the turbine, which is mechanically coupled to an axial flow fan. The fan is used to impel ram air through the heat exchanger and an overboard exhaust duct. Pressure reduction and final heat loss occur as a result of energy loss and expansion of bleed air as it passes through the turbine.

Wool wicks, with one end submerged in MIL-L-23699 oil, transmit lubricant to the bearings supporting the common shaft of the turbine and fan assembly. A sight gauge on the turbine housing is used to check the oil level.

Two overtemperature indicators are installed on the turbine. Each sensor probe head holds down a spring-loaded pop-up stem with an eutectic solder alloy. If the air in the passage reaches the melting point for the solder alloy, the indicator head pops up and stays exposed to alert maintenance personnel that the cooling turbine has been exposed to an excessive temperature level and needs to be replaced. The probe in the turbine inlet is set to trip at 21710F, and the probe in the fan inlet will trip at 45010F. Obstructions or collapse of the ram air inlet duct is the most likely cause of actuating this indicator.

HEAT EXCHANGER CORE, UPPER AND LOWER PLENUMS.- The heat exchanger lower plenum (2) contains the ducting for the ram air inlet and outlet. Cooling ram air (4) flows into the lower plenum and through the heat exchanger core (3) and out through the overboard exhaust duct (6) to the upper plenum, or to the ram air augmentation subsystem (5).

The heat exchanger upper plenum, which supports the turbine and fan assembly (1), is mounted on the opposite side of the heater core. Ram air drawn through the heater core for cooling purposes is diverted to the heat exchanger exhaust duct through the heat exchanger upper plenum. The heat exchanger core is the air-to-air heat sink, and it uses ram air to cool the bleed-air supply.

NONICING AND LOW-LIMIT CONTROL MODULATING VALVE.- The nonice and lowlimit control valve maintains conditioned airflow through the water separator by adding bleed air at the mixing muff to prevent water separator

Figure 4-7.-Refrigeration package and water separator.

icing. (See figure 4-8.) Ice forming on the wire screen at the water separator discharge duct is detected by two pneumatic pickups located just before and after the water separator. These pickups sense a differential pressure across the water separator. If differential pressure is sensed across the water separator, the nonice and lowlimit control valve will remain open until the temperature of the inlet air to the water separator is high enough to melt collected ice. When the ice is melted, the pressure differential returns to normal. In addition, the refrigeration pack lowlimit control electrically signals the nonice and low-limit control valve when separator outflow drops to 0F.

REFRIGERATION PACK LOW-LIMIT CONTROL.- The refrigeration pack low-limit control (fig. 4-6) is located in the ECS compartment. It is mounted downstream from the water separator in a 6-inch duct of cooled discharged bleed air.

The refrigeration pack low-limit control uses 28-volt dc power to energize its circuitry. A thermistor senses duct air temperature and compares it with an internally generated reference. The difference is amplified to modulate a torque motor in the nonice and low-limit control valve. (See figure 4-8.) The torque valve controls the regulated air supply (3) with a flapper valve (1), which controls the diaphragm pressure in a

butterfly actuating linkage (12). The nonice and low-limit control valve can be returned to the differential pressure control mode by opening the cabin temperature high-limit thermostat (4). This causes the upper chamber (6) of the switcher valve (7) to be vented (17) and returned to its primary

position. A check valve (5) is provided to prevent extraneous signals from affecting the nonice and low-limit control valve.