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