Magic-pak question

Scroll compressor noise

A couple of background statements before we delve into the matter at hand.

Reciprocating compressors operate with a piston (or series of psitons) moving back and forth within the compression cylinder. At the top of the cylinder are two valves; a suction valve and a discharge valve.

There are four mini-porcesses that take place in the reciprocating compressor. They are expansion, suction, compression and discharge. During expansion and compression, both the suction and discharge valves are in the closed position. During suction, the suction valve is open and the discharge valve is closed. During discharge, the discharge valve is open and the suction valve is closed.
When the compressor is off, both valves are closed. THE SUCTION AND DISCHARGE VALVES ARE NEVER OPEN AT THE SAME TIME. This fact prevents the refrigerant pressures from equalizing through the compressor when the system cycles off.

Unlike reciprocating compressors, scroll compressors are made up of two nesting scrolls: one is stationary while the other wobbles or orbits. As the orbiting scroll wobbles, refrigerant is pushed toward the center of the nested scrolls where the volume the refrigerant occupies is greatly decreased.

Scroll compressors do not utilize valves and, for that reason, allow the refrigerant pressures to rapidly equalize when the compressor cycles off.

So, in a nutshell, the sound you hear is the sound of the system pressures equalizing when the compressor cycles off. At times, this sound can be quite loud and can resemble the sound of rustling a handful of marbles between your palms.

I hope this helps.