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.

CAUTION

To warm refrigerant containers or cylinders for more rapid discharge, use care to prevent a temperature above 120F because the fusible plugs in the cylinder and valve have a melting point of about 157F.

Figure 6-52. - Connections for drawing a vacuum.

EVACUATING AND CHARGING A SYSTEM

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.

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:

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 6-37