GMC 1976 ZEO 6083 Maintenance Manual page 741

24E- 2 ROOF MOUNTED AIR CONDITIONER
COURTESY OF COPELAND CORPORATION
A 1773
Figure 3-Compressor (Typical)
the refrigerant through the suction line from the
evaporator .
It has a piston connected to the motor shaft by
a connecting rod. The valves are reed type like those
used in two cycle gasoline engines . The oil has been
refined for a very low moisture and wax content to
make it suitable for use in compressors . The com-
pressor has motor, start, and run windings plus an
overload switch .
CONDENSER (FIGURE 2)
The condenser transfers heat from the high pres-
sure, high temperature, refrigerant gas inside the
tubes to the outside air flowing across the fins . As the
refrigerant gives up heat, its temperature decreases
until, at this pressure, it reaches the point at which
the gas condenses into a liquid . The liquid refrigerant
then leaves the condenser and is forced through the
capillary tube into the evaporator coil .
CAPILLARY TUBE (FIGURE 4)
The capillary tube is a metering device for con-
verting high pressure liquid refrigerant into low pres-
sure liquid refrigerant . It is a long thin copper tube
from the evaporator to the condenser. The refriger-
ant charge is critical . Precise charging of an exact
amount is required . Excess refrigerant will cause unit
Figure 4-Capillary Tube (Typical)
to frost back on the low or suction side during off
cycle.
EVAPORATOR (FIGURE 2)
Refrigerant-22 will boil at low temperature when
it is under low pressure . In the evaporator at 70 psi
gauge pressure, it will boil or vaporize at about 40°F.
(4.4° C.) The vehicle interior air being blown across
the fins of the evaporator by a fan or blower will lose
its heat to the cold liquid refrigerant as the latter
rapidly changes to a gas.
A typical air conditioning system is shown in
Figure 5.
ELECTRICAL COMPONENTS
(FIGURES 6 and 7)
BLOWER SWITCH (MARK IV)-Rotary type with high
fan, low fan, high cool, low cool, and off positions.
BLOWER SWITCH (DUO-THERM)-Rotary type with
high fan, medium fan, low fan, high cool, medium
cool, low cool, and off positions.
THERMOSTAT-Return air sensing type to control in-
side vehicle temperature and prevent evaporator
freeze up .
POTENTIAL (OR START) RELAY-After starting unit,
closed points will open, breaking electrical current