52 Auto Heating & Air Conditioning
Note: Vacuum pumps and charging scales
are not dedicated units. Their operating
procedures and settings may, however, be
different for different refrigerants.
Combination Machines
Many modern machines are combination machines.
A combination machine combines many of the compo-
nents discussed in this chapter into a single unit. Most
combination units have gauges, vacuum pumps, storage
tanks, charging scales, and various refrigerant pressure
and contamination indicators. The operation of these units
is the same as for individual units. However, selecting
switches at the combination machine control console
performs all of their functions.
Flushing Equipment
Occasionally a contaminated refrigeration system must
be fl ushed. There are two ways to fl ush a system, open and
closed loop. Open loop fl ushing is done with an air-oper-
ated blowgun, while closed loop fl ushing is performed with
special fl ushing equipment. Both types are explained in the
following paragraphs.
Air-operated Guns
An air-operated rubber tip blowgun, Figure 3-28, is
often used for open loop fl ushing. Some versions of the
blowgun use a tank and hose design that injects the solvent
into the system using air pressure, Figure 3-29. Open loop
fl ushing is always done with refrigerant compatible sol-
vents. To use an air-operated gun for fl ushing, recover the
refrigerant and disconnect the fi ttings from the component
to be fl ushed. Attach a drain hose to the inlet opening of
A
Figure 3-26. A—This oil injector uses a screw operated piston to
push oil into the refrigeration system. B—This oil injector makes
use of the pressure difference between the high and low sides
of the refrigeration system. (General Motors)
High Low
Gauge set
Oil injector
cylinder
Compressor
Compressor
fittings assembly
Hook to
compressor
(low side)
Hook to
compressor
(high side)
Vacuum
B
Figure 3-27. Dedicated HVAC service machines can perform
all refrigeration service operations for one type of refrigerant.
The R-12 machine is red, the R-134a machine is blue.
Figure 3-28. A blowgun can be used to open fl ush the refrigera-
tion system and is often used generally for removing debris from
air intakes and evaporators. Always wear eye protection when
using a blowgun.