TM9-4120-400-1
4
Section Ill TECHNICAL PRINCIPLES OF OPERATION
1-11. REFREIGERATION CYCLE.
The COMPRESSOR (1) 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 (3A) and (3B)
and RECEIVER (4).
The condenser fan draws outside ambient air over and through the two section CONDENSER
COIL (3A) and (3B). The high temperature, high pressure gas from the COMPRESSOR (1) is cooled by the flow
of air and is changed into a high pressure liquid.
The LIQUID SIGHT GLASS (5) indicates the presence of moisture and quantity of refrigerant in the
system.
The DEHYDRATOR, DESICCANT, REFRIGERANT (filter/drier) (6) removes any moisture (water vapor)
or dirt that may be carried by the liquid refrigerant.
The SOLENOID VALVE (7) is controlled by the TEMPERATURE SELECTOR on the control panel.
This valve will shut off the flow of refrigerant to the evaporator section when the temperature in the conditioned
area reaches the set point.
The EXPANSION VALVE (8) controls the amount and pressure of liquid refrigerant to the
EVAPORATOR COIL (9). The EXPANSION VALVE (8) senses the temperature and pressure of the refrigerant as
it leaves the evaporator coil. By use of the sensing bulb, the valve constantly adjusts the flow of liquid refrigerant
to the EVAPORATOR COIL (9).
As the liquid refrigerant leaves the EXPANSION VALVE (8) it enters the EVAPORATOR COIL (9). As
the Iiquid 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 or "flash" to a gas. The evaporator blower circulates the warm air
from the conditioned space over and through the evaporator coil. Liquid absorbs heat when it changes from a
liquid to a gas. As air from the conditioned spaces comes in contact with the EVAPORATOR COIL (9), the air is
cooled.
To prevent compressor overload and damage during start-up, SOLENOID VALVE, pressure
equalizing (15) is closed at start of cooling cycle. This valve opens when compressor is not running to equalize
pressure on both sides of compressor.
b. Bypass System. This unit has a bypass system which allows cooling operation at low cooling loads without
cycling the compressor on and off. In bypass the refrigerant is piped from the discharge to the suction side of the
compressor, bypassing the EVAPORATOR COIL (9).
When the TEMPERATURE SELECTOR on the control module senses that cooling conditions have
reached the set point, it closes the SOLENOID VALVE (7) to shut off refrigerant flow to the EVAPORATOR
COIL (9).
As the compressor suction pressure starts to drop, the PRESSURE REGULATOR (10) opens to allow
flow of hot gas from the compressor.
The QUENCH VALVE (16) senses the temperature of the gas at the suction side of the compressor.
To prevent excessively hot gas from reaching the compressor the QUENCH VALVE (16) opens to allow liquid
refrigerant to mix with the hot gas.
The LINEAR ACTUATING CYLINDER ASSEMBLY (14) automatically controls the condenser
discharge louver assembly.