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20 TRG-TRC004-EN
notes
period two
Compressor Capacity Control
In response to an increasing load, the controller sends a signal to close the
solenoid valve. This closes the port that allows the pressurized refrigerant
vapor to travel to the top of the unloader valve. A controlled leakage rate
around the unloader valve relieves the pressure, allowing the valve to open and
refrigerant vapor to once again flow to the cylinder to be compressed.
Another type of cylinder unloader uses either pressure or electrically-actuated
valving mechanisms to hold open the suction valve of the piston–cylinder pair.
Since the suction valve is prevented from closing, no compression occurs in
that cylinder and the discharge valve does not open. Still other types of cylinder
unloaders divert the compressed refrigerant vapor back to the suction side of
the compressor. In contrast to the cylinder unloaders shown, these other
methods expend energy in moving refrigerant vapor during both the upward
and downward piston strokes within the unloaded cylinders.
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Figure 30