Most of these parts go in larger and variable capacity systems. With larger systems, these are used to head problems off at the pass.
Filter-dryers are (99% of the time) installed in the liquid line to keep the refrigerant and oil clean, as well as scavenge any stray moisture that may exist in the system. Any time the refrigerant system is opened, the filter is changed as cheap insurance against big deadly problems.
Liquid Receivers and suction accumulators are vessels that buffer what is downstream from them from what they shouldn't be fed. Receivers feed expansion valves liquid, accumulators feed compressors gas. These vessels also act as reservoirs for excess refrigerant in the system. With heat pumps, the reverse cycling sometimes causes a full condenser to "burp" its charge into the low side of the system as it depressurizes. A suction accumulator catches this "spew" before it can reach the compressor inlet.
Many larger systems have multiple evaporators and condensers. When these "extra" heat exchangers come online or offline, the required refrigerant amount changes, so the "extra" refrigerant is stored in or drawn from these vessels.
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