Commercial refrigeration units are equipped with permanent service (access) valves, which make the service technician’s job much easier. With these valves already in place, installation of piercing valves becomes unnecessary. Some units come with a valve installed directly on the compressor suction opening (see figs. 100 and 118) and one connected to the receiver (see figs. 101 and 118). Many bolted-type compressors are equipped with suction and discharge valves connected to the compressor housing (fig. 120). The valves seal off the system (by turning the valve stems all the way clockwise) and trap the refrigerant in the sealed system. By removing the bolts connecting the valves to the compressor housing, they can be removed and reconnected to the new compressor in a few minutes without breaking into the sealed system and having to do the regular procedures of evacuating, recharging, and installing a new filter-drier. In most belt-driven compressors (see figs. 31 and 32), these valves are also mounted directly on the high- and low-side ports of the compressor. To gain access to the system,
1. remove each valve stem cap and each gauge line access cap;
2. connect the compound gauge
to the low-side valve and the high-pressure gauge to the high-side valve; and
3. using a service wrench, turn the valve stems to open the lines to the gauges.
In figure 102, you can see the different positions of the stem. When the stem is all the way in, the condenser or suction line is blocked, depending on whether the valve is installed on the suction or discharge line. When the stem is turned counterclockwise all the way out, the gauge connection is blocked. This is the position it must be in when disconnecting the gauges.
When the stem is in its midposition, the path is opened to the suction or discharge line and to the gauge manifold as well as the compressor. So then, every port is open. When the stem is all the way in, it closes the suction or discharge line and leaves the compressor and gauge ports open.