| Evacuating and Charging a System One of your jobs 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
Evacuation
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
obtained
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
Charging
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:
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 the line with gas and clears the air from the line. After
clearing, tighten the connection
Connect a line from the LOW (LO)
valve (suction) on the gauge manifold set to the suction service valve of the compressor
Start the compressor
Open the valve on the cylinder and
the LOW (LO) valve (suction) on the gauge manifold set
Open the suction service valve on
the compressor to permit the gas to enter the compressor where it will be compressed and
fed to the high side. Add the refrigerant slowly and check the liquid level indicator
regularly until the system is fully charged. It is easy to check the receiver refrigerant
level in some makes of condensing units because the receiver has minimum and maximum
liquid level indicator valves which show the height of the liquid level when opened. If a
liquid line sight glass is used, the proper charge may be determined when there is no
bubbling of refrigerant as it passes by the glass. The sight glass will appear empty
Again, be certain the refrigerant
cylinder is in the vertical position at all times; otherwise, the liquid refrigerant will
enter the compressor and, liquid not being compressible, damage the piston or other parts
of the compressor |
