Liquid-To-Air Heat Exchanger

pump, a ram air valve, a ground cooling fan, a coolant filter, a low-pressure sensor, a high- temperature sensor, a coolant temperature sensor, and an airflow valve. Liquid-To-Air Heat Exchanger The liquid-to-air heat exchanger extracts heat from the liquid coolant that flows through the two pass counter flow channels within the heat exchanger. A single-pass air circuit dissipates heat extracted by the heat exchanger. A thermostatic temperature control valve, mounted in the inlet/outlet manifold of the heat exchanger and set in parallel with the heat exchanger core, senses coolant temperature. The control valve mixes bypass and core fluid to maintain a delivery temperature of 80° to 90°F (27° to 32 °C) to the radar transmitter. In the cold position (bypass valve fully closed), a bleed flow of 0.05 to 0.10 gpm is provided to aid in purging the core during system servicing. Liquid Coolant Pump The liquid coolant pump assembly is a self- priming, submerged, centrifugal pump with a cylindrical two-section reservoir and a fill level gauging mechanism. Air bleeding of the reservoir is done by manually actuating a bleed valve connected to the reservoir. The guaging mechanism in the pump unit combines inputs from coolant temperature and reservoir piston position to change a fluid level indicator on the service panel and supply a signal to the Digital Display Indicator to latch a fluid low code. Ram Air Valve An actuator opens and closes the ram air valve. The motor is switched off at the end of each stroke by internal limit switches, which also set up circuitry to reverse actuator travel upon the next power application. The actuator drives the valve closed when a ground is supplied through either a weight on wheels relay or the air data computer when ram air is hot. The actuator drives the valve open when both grounds are lost. A failure in the actuator operation causes a weapons system fail code to latch in the Digital Display Indicator in the nosewheel well. Ground Cooling Fan The ground cooling fan is electrically powered and supplies a flow of ambient air for heat transfer from the liquid cooling heat exchanger during aircraft ground operations. Coolant System Filter Coolant is filtered before passing through the radar transmitter. When the replaceable filter element is contaminated, resulting differential pressure will extend a manually reset indicator on the filter assembly, providing a visual contamination indication. Low-Pressure Sensor The low-pressure sensor located in the coolant line provides a ground to the maintenance status display and recording system until coolant pressure falls below preset limits. The loss of ground causes a weapon system fail code to latch in the Digital Display Indicator. High-Temperature Sensor The coolant high-temperature sensor, located in the coolant line, provides a ground to the maintenance status display and recording system until coolant temperature rises above preset limits. The loss of ground causes a weapon system fail code to latch in the digital display indicator in the nosewheel well. Coolant Temperature Sensor The coolant temperature sensor located in the coolant line provides coolant temperature readings to the ACS temperature/flow controller, allow- ing the controller to modulate the airflow valve. Airflow Valve The radar liquid cooling airflow valve is pneumatically modulated to limit, as necessary, conditioned air to the heat exchanger. The ACS controller supplies electrical power to the airflow valve torque motor, which controls pneumatic pressure to the airflow valve. The valve is spring- loaded closed. 1-21