In addition to the five main components we have just described, a refrigeration system requires several controls and accessories. We will briefly describe the most important ones.

DEHYDRATOR

A dehydrator, or dryer, containing silica-gel or activated alumina, is placed in the liquid refrigerant line between the receiver and the TXV. In older installations, bypass valves allow the dehydrator to be cut in or out of the system. (See fig. 16-3, insert A.) In newer installations, the dehydrator is installed in the liquid refrigerant line without any bypass arrangement. (See fig. 16-3.)

MOISTURE INDICATOR

A moisture indicator is located either in the liquid refrigerant line or is built into the dehydrator as shown in figure 16-13. The moisture indicator contains a chemically treated element that changes color when there is an increase of moisture in the refrigerant. In an R-12 system, the indicator shows pink when the moisture level is too high; it shows blue when the moisture level is satisfactory. The color change is reversible and should change back to a DRY (blue) indication after the moisture has been removed from the

Figure 16-13.-Refrigeration dehydrator with moisture indicator.

refrigerant. If excessive moisture or free water comes into contact with the moisture indicator element, the indicator will no longer register pink for wet, but will be light gray in color. It will no longer change color and must be replaced.