modulating valve opens. This valve varies the amount of hot air from the 400°F bleed manifold temperature control system used to warm the coolant fluid. When the heat exchanger outlet fluid temperature reaches 104°± 4°F and the missile outlet fluid temperature reaches 85°±3°F, the hot air modulating valve will close. This prevents the cold and hot air modulating valves from being open simultaneously. The missile supply line sensor, located at the outlet of the heat exchanger, is also used to sense an overtemperature condition. If the coolant temperature exceeds 115°± 3°F, the missile con- dition (MSL COND) advisory indicator light il- luminates. The hot or cold air modulating valve will close. If the missile pump pressure drops to 60±5 psi, a pressure switch causes the MSL COND light to illuminate. If pressure downstream of the pump increases to 89±5 psi, the missile bypass valve opens to return the fluid to the pump inlet. The missile cooling system consists of a cold air modulating valve, hot air modulating valve, air-to-coolant heat exchanger, coolant pump, coolant fluid expansion tank, bypass valve, air- moisture-contaminant remover, controller, coolant temperature sensor, fairing interlock switch, and liquid cooling control panel. Each of these components is discussed in the following paragraphs. The functional relationship of the components is represented in figure 1-18. Missile Cold Air Modulating Valve The cold air modulating valve is mounted on the air-to-coolant heat exchanger. It varies the flow of refrigeration system air to the heat exchanger. The valve has a butterfly, a diaphragm-type pneumatic actuator that is mechanically linked to the butterfly, an electro- magnetic torque motor, and butterfly position switches. Electrical signals from the missile controller govern the torque motor, which allows regulated air pressure to be vented. The smaller the amount of air pressure vented, the larger the valve opening. If the electrical power or air pressure is interrupted, the valve closes. Missile Hot Air Modulating Valve The missile hot air modulating valve is mounted on the air-to-coolant heat exchanger. The valve varies the flow of hot air from the 400°F bleed manifold temperature control system in response to electrical signals from the controller. The hot air heats the coolant during system warm- up. The operation of the valve is the same as the missile cold air modulating valve. Missile Air-to-Coolant Heat Exchanger The air-to-coolant heat exchanger consists of two sections: weapons control system (radar) loop, and missile loop. The heat exchanger is similar to an automobile radiator. The coolant flows through the core while air flows around the core. When the radar portion of the heat exchanger is being used, the missile cold and hot air modulating valves are closed to prevent reverse flow through the missile section. Missile Coolant Pump The coolant pump is a single-stage, centrifugal pump driven by a low-slip, two-pole induction motor. When the pump is operating, it circulates 18 gallons of coolant per minute through the system. The pump is lubricated and cooled by a small portion of the coolant, which is circulated through the motor. A pressure switch in the pump outlet opens when the pump output pressure drops to 60 ±5 psi. The pressure switch causes the MSL COND (missile condition) advisory light to illuminate. Also, a thermal switch will open when 230°±5°F is reached. This switch causes the pump to stop and also illuminates the MSL COND light. The coolant pump is located in the right Phoenix fairing. Coolant Fluid Expansion Tank The expansion tank is located in the right Phoenix fairing. The tank maintains a constant coolant fluid pressure at the pump inlet, accommodates thermal expansion of the coolant, and provides a coolant reserve for the missile loop in case of leakage. The tank has a bellows, fluid sight and level indicator, fluid relief valve, and a pneumatic pressure indicator. The bellows is pressurized to maintain a positive fluid pressure of 30 to 37 psi at the pump inlet. Should pressurization reach 45.0±2.3 psi, the fluid pressure relief valve will open and vent fluid. The fluid sight and level indicator displays fluid level, and the pneumatic pressure indicator extends to indicate air pressure by temperature degrees. 1-25