Section I. DESCRIPTION AND USE OF OPERATOR'S CONTROLS AND INDICATORS
2.1. Operator's Controls and Technical Principles of Operation
Before turning on any of the air conditioner's operating controls, make sure that the fabric cover is rolled
up and secured, and that evaporator intake and discharge grilles are fully open.
The compressor crankcase heater must be energized at least 4 hours before the compressor is allowed to
start. Liquid refrigerant and oil migration to the compressor crankcase can cause severe damage to com-
pressor instantly on startup in this condition. This condition and damage can be prevented by applying
power to unit at least 4 hours prior to startup of compressor. The crankcase beater will vaporize liquid
refrigerant in compressor crankcase where energized and allowed enough time to heat compressor to cut
out temperature of crankcase heater thermostat. Unit may be operated in ventilation mode during time of
crankcase beating which will prove power is applied to unit. When this unit is used with an enclosure that
has a main circuit breaker and an air condition circuit breaker and is connected to a continuous power
source, the two circuit breakers should be left in on position so compressor will stay at operation tempera-
ture and ready for instant use without danger of severe damage at startup.
a. Control Panel The control panel is the small rectangular panel located in the upper middle part of the lower
panel. It contains the following operating controls. (See figure 2-1).
(1) Mode Selector Switch. The mode selector switch is a rotary, five-position switch on the right hand side of
the control panel. The positions are marked OFF, VENTILATE, COOL, LO HEAT and HI HEAT.
(a) Ventilating Mode. When the mode selector switch is set at VENTILATE, only the two-speed fan will
operate. Volume of airflow can be varied to either HI SPEED or LO SPEED by setting the two-speed fan switch on the
control panel to the desired position. Outside air can be admitted through the fresh sir damper, controlled by a pull-chain
located about halfway up the left side of the sir conditioner.
The air conditioner can be equipped for operation in chemical-biological-radiological (CBR) environ-
ment by connecting filtering equipment to the rectangular covered opening at the upper left side of the rear
surface of the unit.
(b) Cooling Mode. When the selector switch is set at COOL, power is connected to the two-speed fan, the
compressor, and the various controls and relays needed to operate and control the refrigeration system. When the tempra-
hue control thermostat is turned to a setting below the ambient temperature in the room, the typical cooling cycle begins to
operate in the following manner. (See refrigeration diagram, figure 2-2).
1 Cooling Cycle. Cooling takes place when the liquid refrigerant changes to vapor in the evapora-
tor coil (12). This change from liquid to vapor absorbs heat from the air passing over the outside surfaces of the evaporator
coil. thereby cooling the air. The vaporized refrigerant is piped from the evaporator coil (12) to the compressor (1) where it is
increased in density and temperature. The compressed vapor is then piped to the condenser coil (2A) where air passing over
the outside surfaces of the coil extracts the heat of evaporation and compression from the vapor, thereby recondensing it to a
liquid. The liquid refrigerant flows through a filter-drier (7) and the sight-glass liquid indicator (9) as it goes to the expan-
sion valve (10) which meters the refrigerant into the evaporator coil to repeat the cycle. A pressure regulating valve (15)
prevents the development of too low a pressure in the compressor suction line, by opening at a preset pressure to adjust
compressed vapor into the suction line. Pressure switch (17) closes at a preset pressure to override the manual two-speed fan
switch if set at LO SPEED.