PRINCIPLES OF OPERATION. - TM-5-4120-339-140016

TM 5-4120-339-14

(2) The compressor is a motor driven unit which is used to pump refrigerant through the system. The high

pressure cut-out switch stops the unit if the compressor discharge pressure rises above 460 psig (32.3 ks/cm2).

(3) The refrigerant, in a gaseous vapor state, is pumped by the compressor to the condenser coil. As the

refrigerant flows through the condenser coil, the condenser fan draws outside air into the condenser coil area and

exhausts it back outside. This action serves to change the refrigerant from the gaseous vapor state into the liquid state.

(4) The refrigerant, in the liquid state, flows from the condenser coil to the evaporator coil. The evaporator

fan draws air from the conditioned area and blows it across the evaporator coil. Refrigerant within the evaporator coil

absorbs heat from the circulating air. The cooled air is then blown into the conditioned area by the evaporator fan.

(5) The absorption of heat by the refrigerant as it passes through the evaporator coil, causes the refrigerant

to change from the liquid state back into the gaseous vapor state. The vaporized refrigerant is then routed to the suction

side of the compressor.

(6) As the evaporator fan blows cooled air into the conditioned area, the temperature gradually decreases.

When the temperature in the conditioned area falls below the setting of the thermostat, the cooling section is automatically

switched to the by-pass mode. In this mode, the fan motor and the compressor continue to operate, but the refrigerant is

routed through a by-pass circuit, so that the evaporator fan no longer blows cooled air into the conditioned area. When

the temperature in the conditioned area again rises above the setting of the thermostat, the by-pass circuit is automatically

shut off and the refrigerant again flows through the cooling circuit, causing cooled air to he blown into the conditioned

area. When the air conditioner is operating in the "COOL" setting, the fan motor and the compressor are operating

continuously, either in the cooling mode or in the by-pass mode. This feature allows the unit to present a constant

electrical load to the power supply.

c. Heating. The heating section consists primarily of six electrical resistance heaters. High heat is provided

when the selector switch is set to the "HI HEAT" position. In this position, all six of the heater elements are energized.

Low heat is provided when the selector switch is set to the "LO HEAT" position. In this position, only three of the heater

elements are energized. Heat is blown into the conditioned area by the evaporator fan. The heater elements are under

the control of the thermostat which serves to maintain the temperature in the conditioned area at the desired level.

d. Ventilation. The fan motor starts when the selector switch is placed in the "VENTILATE" position. The

evaporator fan draws air from the outside and blows it into the conditioned area.

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