valve (33) is installed in the line to permit cold liquid
gives up heat to return to a liquid. Refer to figure 11-21
refrigerant to be added to the hot gas to lower the
as you study the refrigeration cycle of the A/M32C-17.
temperature of the hot gas. A hot gas solenoid valve
The compressor (1) converts low-pressure gas
(29) is installed in the line to allow the unit to "pump
(R-22) from the three evaporators (14, 15A, 15B) into
down" when the cooling system is turned off.
high-pressure gas. This hot, high-pressure gas is then
In addition to the hot gas bypass system, the
passed into the condenser coil (4A, 4B).
compressor is equipped with automatic internal
The hot high-pressure gas is cooled by the
unloaders. An unloader is a device that causes the
condenser airflow and condensed into high-pressure
compressor's internal suction valves to be lifted from
liquid. The liquid then passes to and is stored in the
their seats, which allows equalizing high-side and
receiver tank (5).
low-side pressures for a brief time during starting, and
The liquid refrigerant passes from the receiver tank
for controlling compressor capacity. As more
(5) through the drier-strainer (10), subcooler (heat
refrigerant is demanded, this unloading process is
exchanger) (9), solenoid valves (27, 28), and sight
reversed until the compressor is delivering its
glasses (11A, 11B). A portion of the liquid is passed
maximum output.
through an expansion valve (26) and is circulated
Ventilate Mode
through the subcooler (9) to aid in the cooling of the
liquid refrigerant.
Since the ventilating blower is belt-driven directly
The subcooled liquid refrigerant is metered by the
from the engine drive shaft on the input side of the
expansion valves (12A, 12B, 13, 32). These valves
clutch, the blower operates whenever the engine
meter the refrigerant flow and reduce the pressure of the
operates. When the selector switch is moved to
refrigerant so that the liquid refrigerant enters the three
START-VENTILATE, the ventilating blower draws
evaporators (14, 15A, 15B) as a cold low-pressure
ambient outside air through the inlet air filter and blows
mixture of liquid and vapor.
the air into the conditioned area. A damper inside the
housing in the air inlet plenum provides a means of
The cold, low-pressure mixture of liquid and vapor
airflow control.
absorbs heat from the air passing over and through the
three evaporator coils. In the process of absorbing the
Dehumidify Mode
heat, the refrigerant evaporates to a low-pressure gas.
The low-pressure gas is drawn to the suction side of
Moving the selector switch to the DEHUMIDIFY
the compressor (1) where the refrigeration cycle starts
position starts the refrigeration cycle. Running in the
over.
dehumidify mode, however, the unit uses only the
The aftercooler evaporator coils (15A, 15B) each
precool evaporator. The air is cooled enough to reduce
have a thermostat-controlled solenoid valve (27, 28).
its moisture content, and then warmed during its
These solenoid valves open and close depending upon
movement through the blower.
air temperature at the outlet of the unit. Output air
temperature is controlled by the opening or closing of
Pump Down Mode
one, or both, aftercooler solenoid valves. The
thermostat bulb for the aftercooler evaporators is
The pump down function is used to shut down the
located at the air outlet to the conditioned area.
refrigeration cycle prior to securing the air-conditioner
or at any time the system must be opened. When the
The A/M32C-17 has a hot gas bypass system to
selector switch is in the PUMP DOWN position, the
permit recirculation of compressor discharge gas. This
three evaporator solenoids close, and the system
system automatically induces an artificial load to match
continues to pump the refrigerant into the receiver until
the evaporator's load. When the hot gas pilot valve (30)
the low-pressure cutout stops the compressor. At that
senses that the suction pressure has dropped below a
point, most of the refrigerant is contained in the
preset point, it opens the hot gas pressure regulator (31)
receiver.
to permit hot gas to bypass the compressor. A quench
11-22
