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Control of Liquid Refrigerant Floodback to the Compressor
During Operation
Liquid floodback during operation (see Figure 6-9) can be caused by fan failure or dirty
clogged filters that can reduce the heat transfer rate to such a point that the liquid refrigerant
floods through instead of vaporizing. When this situation occurs, liquid refrigerant may enter
the compressor under conditions that result in separation of the oil and refrigerant. This
separation may result in an accumulation of the refrigerant under the oil (see Figure 6-10). Thus,
when the compressor is started, the first liquid to be pumped to the bearings will probably be
refrigerant, not oil. Even if this oil-refrigerant separation does not occur, the large amount of
liquid refrigerant in the crankcase will instantly vaporize and boil away the oil charge when the
compressor starts (see Figure 6-11) thereby leaving the compressor oil-starved for many seconds
(see Figure 6-12).
High Pressure Gas
High Pressure Liquid
Low Pressure Liquid
Low Pressure Gas
Fan Fan
Evaporator
Condenser
Compressor
Expansion Device
Filter
FIGURE 6-9: Liquid refrigerant floodback to the compressor.
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