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AIR CONDITIONER SYSTEM
COMPONENTS
COMPRESSOR (Refrigerant Pump)
The compressor separates the low pressure and the
high pressure sides of the system. It concentrates the
refrigerant returning from the evaporator (low side)
creating a temperature much higher than the outside
air temperature. The high temperature differential be-
tween the refrigerant and the outside air is necessary
to aid rapid heat flow in the condenser from the hot
refrigerant gas to much cooler outside air.
To create high pressure concentration, the compres-
sor draws in refrigerant from the evaporator through
the suction valve and during compression strokes,
forces it out through the discharge valve to the con-
denser. The pressure from the compressor action
moves the refrigerant through the condenser, receiver-
drier and connecting hoses to the expansion valve.
The compressor is driven by the engine through a
v-belt driving an electrically operated clutch mounted
on the compressor drive shaft.
SERVICE VALVES
Quick-connect hose end fittings with integral service
valves attach to system service ports for servicing the
unit. A manifold gauge set is connected into the system
at the service valve ports and all procedures, such as
discharging, evacuating and charging the system, are
performed through the service valves.
CONDENSER
The condenser receives the high pressure, high-tem-
perature refrigerant vapor from the compressor and
condenses it to high pressure, hot liquid.
It is designed to allow heat movement from the hot
refrigerant vapor to the cooler outside air. The cooling
of the refrigerant changes the vapor to liquid. Heat
exchange is accomplished using cooler air flowing
through the condenser. Condenser cooling can be with
ram air provided by vehicle movement and sometimes
aided by electric or hydraulic fans or by using the air
movement provided by the radiator fan.
Ram air condensers depend upon the vehicle move-
ment to force a large volume of air past the fins and
tubes of the condenser. The condenser is usually lo-
cated in front of the radiator or on the roof of the truck.
M9-4
Condensing of the refrigerant is the change of state of
the refrigerant from a vapor to a liquid. The action is
affected by the pressure of the refrigerant in the coil
and air flow through the condenser. Condensing pres-
sure in an A/C system is the controlled pressure of the
refrigerant which affects the temperature at which it
condenses to liquid, giving off large quantities of heat
in the process. The condensing point is sufficiently high
to create a wide temperature differential between the
hot refrigerant vapor and the air passing over the
condenser fins and tubes. This difference permits rapid
heat transfer from the refrigerant to ambient air.
RECEIVER-DRIER
The receiver-drier is an important part of the air condi-
tioning system. The drier receives the liquid refrigerant
from the condenser and removes any moisture and
foreign matter present which may have entered the
system. The receiver section of the tank is designed to
store extra refrigerant until it is needed by the evapo-
rator. The storage of this refrigerant is temporary and
is dependent on the demand of the expansion valve.
A desiccant is a solid substance capable of removing
moisture from gas, liquid or solid. It is held in place
within the receiver between two screens, which also
act as strainers. Sometimes it is simply placed in a
metal mesh or wool felt bag. Filtering is accomplished
by a separate strainer screen on the pickup tube.
Some sytems may utilize an accumulator instead of a
receiver-drier. If an accumulator is used, an expansion
(fixed-orifice) tube is used instead of the thermostatic
expansion valve described below. When used, the
expansion tube is located inside the inlet tube of the
evaporator and is used to restrict, but still allow a
continuous flow of refrigerant to the evaporator coil.
THERMOSTATIC EXPANSION VALVE
The thermostatic expansion valve controls the amount
of refrigerant entering the evaporator coil. Both inter-
nally and externally equalized valves are used.
The expansion valve is located near the inlet of the
evaporator and provides the functions of throttling,
modulating, and controlling the liquid refrigerant to the
evaporator coil.
The refrigerant flows through a restriction creating a
pressure drop across the valve. Since the expansion
valve also separates the high side of the system from
the low side, the state of the refrigerant entering the
Air Conditioning System
for HFC 134a Refrigerant
M09010 6/97
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