A charging cylinder is a tool that provides the means to place a specific amount of refrigerant into a unit (see p. 112). It is a calibrated cylinder which can measure, in ounces, the exact amount as specified on the nameplate of the unit or in a reference book mentioned on page 112. Before starting to put refrigerant into a charging cylinder, make sure all the valves are closed on the refrigerant cylinder, the charging cylinder, and those on the gauges (see fig. 83).
1. Connect the yellow (center) hose of the manifold gauge to the charging cylinder.
2. Connect the suction (blue) hose to the refrigerant cylinder valve.
3. Place refrigerant canister upside down and turn on its valve. Then turn on the bottom valve of the charging cylinder.
4. Turn on the valve on the compound gauge while watching the scale on the charging cylinder. Keep a hand on that valve. You will see the level of liquid refrigerant rise in the cylinder.
5. Turn off the valve when the cylinder is filled to the desired level (which is the amount specified on the nameplate of the unit being charged). Be certain to use the scale on the charging cylinder that corresponds with the ambient temperature.
6. Turn off the rest of the valves and disconnect the refrigerant tank and the charging cylinder.
HINT: By placing a rubber band around the cylinder at the level of refrigerant you desire before filling it, it will be much easier to spot the place to stop. (See fig. 77).
The valve on top of the charging cylinder is used as a pressure-relief valve. As the cylinder fills, pressure builds inside until it becomes equal to the pressure inside the refrigerant cylinder. At this point, the cylinder stops filling. Relieve some of the pressure by opening the top (relief) valve very little, then close it again. The cylinder will resume filling. (When buying a critical-charge cylinder, be sure to get one with a pressure gauge on top.) When the cylinder is adequately charged, plug in its electrical cord to a 115 V outlet. The cord is connected to the cylinder-heating element. As the element heats, pressure is built up in the cylinder. This pressure is used to force the refrigerant into the unit being charged. NEVER FILL THE CHARGING CYLINDER ALL THE WAY TO THE TOP!
Generally, building up a pressure between 150 and 200 psi is enough for most units. DO NOT ALLOW THE PRESSURE IN THE CHARGING CYLINDER TO EXCEED 275 PSI!
WARNING: When the cylinder is plugged in, do not leave it unattended. It will take a few minutes to build up pressure. Too much pressure will cause the cylinder to explode.
If the amount of refrigerant charge cannot be found on the nameplate, or if for any reason it cannot be determined, get the information from the book Tech Master for Refrigerators and Freezers published by Master Publications, Euclid Street, Santa Monica, California 90404.
The reason the refrigerant cylinder is inverted when filling a critical-charge cylinder is to allow liquid refrigerant to flow into the charging cylinder. If the can is left upright, only vapor refrigerant can be released. Some other refrigerants are quite the opposite; they flow out of the cylinder in the form of liquid when the can is in upright position. Make it a habit to read the instructions printed on the cylinder first.