Fitting gauges
Although the task of fitting gauges is a simple one, it must be realized that any refrigerant has a pressure/temperature relationship: the higher the temperature of the refrigerant, the greater the pressure. It will be seen from the pressure/temperature chart at the end of this manual that any refrigerant, if subjected to even a normal ambient temperature, will generate sufficient pressure to present a danger. Thus the engineer should be conversant with the safety procedures for handling refrigerants, and should observe them.
Open-type system
Service gauges may be fitted when the plant is at rest or when it is operating. In the latter case the high side system pressure will be much greater, and it is recommended that the following procedure be adopted for either condition (Figure 6):
1 Remove the valve caps from the suction and discharge service valves on the compressor.
2 Set both valves to the back seat position.
3 Remove the seal caps from the gauge connections of both service valves (normally a flare nut and bonnet).
4 Fit the blue hose from the manifold to the suction service valve connection.
5 Fit the red hose from the manifold to the discharge service valve connection.
6 Ensure that the centre hose connection on the manifold is capped or that the yellow hose is plugged.