A number of pressure gauges and thermometers are used in refrigeration systems. Figure 16-18 shows a compound R-12 gauge. The temperature markings on this gauge show the boil-ing point (or condensing point) of the refrigerant at each pressure; the gauge cannot measure temperature directly. The fixed pointer (usually red) can be set manually to indicate the minimum or maximum allowable working pressure.

Figure 16-18.-Compound R-12 pressure gauge.

A water pressure gauge is installed in the cir-culating water line to the condenser to indicate the circulating water supply pressure. Standard liquid-in-glass or bimetallic ther-mometers of appropriate range are installed at strategic points within the refrigerant system.