storage cylinder, and then the 1/4-inch valve in the
refrigerant line. When the weight of the service
cylinder shows a sufficient amount of refrigerant is in
the serviced cylinder, close all valves tightly, and
disconnect the charging line at the service cylinder.
To warm refrigerant containers or
cylinders for more rapid discharge, use
care to prevent a temperature above
120°F because the fusible plugs in the
cylinder and valve have a melting point
of about 157°F.
Figure 6-52.Connections for drawing a vacuum.
EVACUATING AND CHARGING A
One of your duties will be charging a system with
refrigerant. If a system develops a leak, you must
repair it first, then charge the system. Similarly, if a
component of the system becomes faulty and must be
replaced, some refrigerant will be lost and the system
will require charging.
Before a system can be charged, all moisture and
air must be eliminated from the components by
drawing a vacuum on the system. To draw a vacuum
on the system, proceed as follows:
1. Connect the portable vacuum pump to the
vacuum fitting on the refrigerant manifold
gauge set (fig. 6-48).
2. Connect the LO line (suction) to the suction
service valve of the compressor, using
appropriate connectors if required.
3. Turn the suction service valve to mid-position,
so vacuum draws from the compressor
crankcase and suction line back through the
evaporator, expansion valve, and liquid line.
When the receiver service valve, condenser
service valve, and discharge service valve are
open, the pump draws back through the receiver
and condenser to the compressor.
4. Attach one end of a 1/4-inch copper tube to the
vacuum pump discharge outlet (fig. 6-52).
Allow the vacuum pump to draw a vacuum of at
least 25 inches. Submerge the other end of the
copper tubing under 2 or 3 inches of clean
compressor oil contained in a bottle.
5. Continue to operate the vacuum pump until
there are no more bubbles of air and vapor in the
oil, which indicates that a deep vacuum has been
6. Maintain the deep vacuum operation for at least
5 minutes, and then stop the vacuum pump.
Leaking discharge valves of a vacuum pump
cause oil to be sucked up into the copper
discharge tube. Keep the vacuum pump off at
least 15 minutes to allow air to enter the system
through any leaks. Then start the vacuum
pump. A leaky system causes bubbling of the
oil in the bottle.
7. Examine and tighten any suspected joints in the
line, including the line to the vacuum pump.
Repeat the test.
In most small refrigerating systems, low-side
charging (fig. 6-53) is generally recommended for
adding refrigerant after repairs have been made. After
the system has been cleaned and tested for leaks, the
steps to charge the system are as follows:
1. Connect a line from a refrigerant cylinder to the
bottom center connection on the refrigerant
gauge manifold set. Be certain the refrigerant
cylinder is in a vertical position, so only
refrigerant in the form of gas, not liquid, can
enter the system. Leave the connection loose
and crack the valve on the cylinder. This fills