A defective expansion valve, refrigerant overcharge, or extremely low load may permit liquid refrigerant to reach the compressor from the evaporator. Because liquids are not compressible, the pistons and valves can suffer damage from such “slugs” of liquid.
To prevent this, you can put a suction accumulator in the suction line between evaporator and compressor. Trapped oil may build up in the bottom of the accumulator after the refrigerant evaporates. Accumulators therefore have an oil return line leading from the bottom of the trap.
This figure shows a cross section of a typical suction-line accumulator. It has a U-tube for passage of refrigerant vapor back to the compressor. The metering port at the bottom of the tube allows oil to return back to the compressor. The metering port is small enough that any liquid refrigerant entering should be boiled off before it reaches the compressor. EXCERPT FROM THE” TECHNICAL INSTITUTE MANUALS “AVAILABLE AT THE ONLINE STORE AT RSES.ORG.