Although the technical schools and many refrigeration manuals refer to high- and low-side float systems, units using these systems are very seldom encountered. The low-side float system was more popular in the early years of mechanical refrigeration. It is also called a “flooded system.” This low side float mechanism is a part of the evaporator. The vapor refrigerant is drawn through the suction line to the compressor then discharged as a high-pressure gas into the condenser where it is cooled and changed to its liquid state. Liquid refrigerant flows into the evaporator through a valve that operates in conjunction with a float. (The lower portion of the evaporator is occupied by liquid refrigerant, while the portion above the float is filled with vapor.) When the desired low temperature is reached, the compressor is de-energized and this operation stops.
Flooded systems are easy to service and are very efficient because the cold liquid refrigerant wets the surface of the evaporator, causing a rapid heat transfer. These systems require a motor that can start under heavy load because the pressures do not equalize during the off cycle. They also take a larger than average refrigerant charge because liquid refrigerant occupies both the liquid receiver tank and the evaporator.
About the only service these units need is the replacement of the needle valve.