Section III. TECHNICAL PRINCIPLES OF OPERATION
a. Cooling cycle. -- Unit operation with mode selector switch set on COOL and the
temperature control thermostat set to DECREASE (cooler).
(1) Compressor (B1) starts.
(2) To prevent compressor overload and damage during start-up, solenoid valve (K4) is
open at start of cooling cycle to equalize pressure on both sides of the compressor.
(3) The compressor (B1) takes cold, low pressure refrigerant gas and compresses it to a
high temperature, high pressure gas. This gas flows through the metal tubing to the condenser
coil (C) and receiver (R1).
(4) The condenser fans draw outside ambient air over and through the condenser coil (C).
The high temperature, high pressure gas from the compressor (B1) is cooled by the flow of air
and is changed into a high pressure liquid.
(5) The refrigerant desiccant dehydrator (filter/dryer) (D) removes any moisture (water
vapor) or dirt that may be carried by the liquid refrigerant.
(6) The liquid indicator (sight glass) (G) indicates the presence of moisture and quantity
of refrigerant in the system.
(7) The solenoid valve (K3) is controlled by the temperature control thermostat on the
control module. This valve will shut off the flow of refrigerant to the evaporator section when
the temperature in the conditioned area reaches the set point.
(8) The expansion valve (V5) controls the amount and pressure of liquid refrigerant to
the evaporator coil (E). The expansion valve (V5) senses the temperature and pressure of the
refrigerant as it leaves the evaporator coil. By use of a sensing bulb and "external equalizer
line" the valve constantly adjusts the flow of liquid refrigerant to the evaporator coil (E).
(9) As the liquid refrigerant leaves the expansion valve (V5) it passes through a
distributor and enters the evaporator coil (E). As the liquid enters the coil at a reduced pressure,
the reduction in pressure and the warmer air being forced across the tubes of the coil cause the
refrigerant to boil and change to a gas (vapor). The evaporator fans circulate the warn-t air from
the conditioned space over and through the evaporator coil. Refrigerant absorbs heat when it
changes from a liquid to a gas. As the air from the conditioned spaces comes in contact with
evaporator coil (E), the air is cooled.
(10) The refrigerant gas is then drawn back to the compressor (B1) and the cycle is