The low pressure switches will close again when the
to 5 psi (.3515 cm), the expansion valve opens,
suction pressure rises to 12 psi (.8436 kg per sq. cm).
admitting liquid refrigerant from the receiver into the
The high pressure switches will close when the
evaporator coil. At this pressure, the liquid refrigerant
discharge pressure drops to 210 psi (14.763 kg per sq.
will boil at approximately -23.3C. (-010F). Since the
cm). The four compressor pressure switches operate
refrigerant is considerably warmer than this when it first
only when the unit is operated manually by either driving
enters the evaporator it begins to absorb heat from its
unit, take care to prevent the suction and discharge
surroundings, until it and the evaporator coil are cooled
pressures from exceeding the normal limits. Two
at approximately -23.3 C. (-10F). From this point on
pressure gages shall be installed on the compressor,
the heat for boiling the refrigerant comes from the
one on the suction side and one on the discharge side
carbon dioxide outside of the evaporator.
so that the suction and discharge pressures may be
refrigerant continues to absorb heat until it is entirely
vaporized and at a temperature approximately the same
as that of the carbon dioxide in the tank.
c. While the refrigerant has been boiling and
Inspect the general condition of the compressor
absorbing heat, it has been moving through the
(fig. 4-85) for cleanliness, freedom from oil leaks and
The final condition, when the
unusual noises during operation. Keep compressor and
refrigerant is entirely boiled away into vapor at the
condenser cooling surfaces particularly clean to
temperature of the carbon dioxide, is obtained just as
maintain full operating efficiency.
the refrigerant reaches the end of the evaporator coil.
From the evaporator, the refrigerant enters the
compressor where the pressure is raised, to cause
attachment, and general freedom from visible damage
or surface corrosion. Check sight glass (1) for adequate
heat in the condenser. Air removes the heat, and the
charge in receiver. To add refrigerant, proceed as
refrigerant is liquefied. Thus, the heat removed from
the carbon dioxide is transferred by the refrigerant to the
a. Install a discharge pressure gage in the
From the condenser, the liquefied
discharge service valve.
refrigerant flows to the receiver to complete the cycle.
b. Connect a full freon cylinder to the gage port(3,
d. When the carbon dioxide has been refrigerated
fig. 4-85), using a charging hose with dehydrator, and a
to the extent that the tank pressure is reduced to 295 psi
(20.7385 kg per sq. cm), the tank pressure switch opens,
c. Before tightening the charging hose connector
breaking the circuit to the driving unit, and the
at the compressor crack the cylinder valve slightly to
compressor stops. While the compressor is idle, the
purge air from the hose.
refrigerant in the evaporator coil will warm up to the
d. Close the suction service valve (2) one turn.
temperature of the carbon dioxide in the tank. This
e. Start the compressor, and slowly admit freon
increases the suction pressure of the refrigeration
from the supply cylinder until the sight glass appears full
system to 11 psi (.7733 kg per sq. cm), which holds the
expansion valve entirely closed, until the compressor
If the compressor pounds, or frost forms
e. The service values shut off the flow of
on the cylinder head, throttle down the
refrigerant when service is required on the system. The
rate of flow of refrigerant with the freon
sight glass permits operation of the refrigerant flow. The
4-90. Pumping Down the System
f. Four compressor pressure switches act as a
The refrigerant must be pumped down
safety device for the compressor.
Two of these
into the receiver when the unit is put in
switches, one for low pressure and one for high
storage, shipped, adding or changing
pressure, are connected with the electric motor circuit
and the other two, one for low pressure and one for high
a. Remove the valve cap (fig. 4-86) and close the
pressure, are connected to the gasoline engine circuit.
receiver liquid outlet valve tightly.
The low pressure switches open to stop the electric
b. Remove the plug from the compressor suction
motor or the gasoline engine at 0O psi suction pressure.
valve (1, fig. 4-87) and install an adapter (2) and
The high pressure switches open to stop the electric
pressure gage, with a range of 30 inches of mercury
motor or the gasoline engine at 240 psi (16.872 kg per
(vacuum) -0 to 100 psi (7.03 kg per sq. cm).
sq. cm) discharge pressure.