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Installation - TM-5-4120-361-14_108
TM-5-4120-361-14 Air Conditioner Vertical Compact 18 000 BTU/HR 208 Volts 3 Phase 50/60 Hz (Model 18K 208 3 60) Manual
Servicing  Refrigerant  System
CHAPTER 6 REPAIR   INSTRUCTIONS Section  I. REFRIGERATION  SYSTEM 6-1. General. The  refrigerant  system,  illustrated by the refrigerant flow diagram (figure 5-1), is a mechanical, vapor cycle type circuit consisting of the evaporator, thermal  expansion  valve,  motor-compres- sor, condenser, and the necessary valves and cutout devices for automatic control during operation. The  thermal  expansion valve releases high-pressure liquid re- frigerant into the evaporator at reduced pressure. The liquid refrigerant begins to vaporize by absorbing heat from the air passing over the external surface of the evaporator coil. The heated vapor is sucked out of the evaporator section by the motor-compressor and forced into the condenser section under high pres- sure where it is cooled and condensed back into a liquid. The heat released during condensation is carried off by the condensing air stream. The liquid refrigerant flows from the condenser to a receiver, to a subcooler, and then to the thermal expansion valve. If the temperature  control  switch  (evaporator return air thermostat) becomes satis- fied, or the evaporator return air tem- perature is lower than the control switch set point, the refrigerant system will switch to a bypass condition. The temperature control switch will activate the normally-open liquid bypass solenoid valve, closing the valve, and therefore shutting off the evaporator section of the unit. The  motor-compressor  will continue to pump as usual and the suc- tion pressure will begin to drop. When it reaches approximately 58 psig (400 kPa), the pressure regulating valve will start to open in an effort to maintain the suction pressure above 55 psig (380 kPa)  (approximately). As the suction temperature increases, due to the pres- sure regulating valve opening, the TM  5-4120-361-14 quench expansion valve will start to meter liquid refrigerant into the suc- tion line in an effort to maintain the suction temperature below 75°F (24°C) (approximately), or 30°F (-1°C) super- heat (approximately). This action (the pressure regulator and quench valve ac- tions) is totally automatic and also may occur at extreme conditions in an at- tempt to maintain the suction pressures (even during the cooling mode) at a condition above 55 psig (380 kPa) and the suction temperatures (measured at the quench bulb well) below 75°F (24°C). The condenser louvers are operated by a refrigerant powered piston located in the high pressure part of the system. This piston should be fully extended (louvers open at 80°F (27°C) - proximately) at 250 psig (1140 kPa) head pressure and fully closed at 165 psig (1140 kPa). Failure to perform this function could result in icing of the evaporator coil and/or cutout on the low pressure cutout. 6-2. Pressure  Testing  the  Refrigerant System. a. General.    A pressure test Will indicate whether the air conditioner is operating at normal or at abnormal pres- sures. When the air conditioner is not operating at normal pressures, the cause should be ascertained and corrected. Refer to table 5-1 for troubleshooting chart. b. System  Pressure  Test.  Remove caps from high and  low pressure service valves (fig. 5-6), connect suction and discharge pressure gages to their re- spective service valves. Compare the gage reading with the normal range of system pressure shown in table 6-1. 6-1

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