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Cooling cycle
Figure 39
is a basic representation of the cooling cycle.
• When the cooling sequence is initiated, the compressor and outdoor fan start. The cooling system is
now in operation. Once the thermostat is satisfied, the system will shut down.
• The compressor pumps out high pressure refrigerant vapor (discharge line). The vapor leaves the
compressor. If the unit is a heat pump, the vapor will pass through the de-energized reversing valve.
• The vapor flows through the discharge line to the outdoor coil. Air from the outdoor fan removes heat
from the refrigerant vapor. When enough heat is removed, the vapor condenses into a high pressure
liquid. The liquid temperature is slightly warmer than ambient air temperature. This warm, high
pressure liquid leaves the outdoor coil and flows through the copper refrigerant line. The liquid passes
through a filter/drier. The filter/drier adsorbs water and filters system contaminants.
• At the end of the line, the refrigerant passes through an Electronic Expansion Valve (EEV), reducing its
pressure and temperature.
• As the liquid, under reduced pressure, enters the indoor coil, it expands and absorbs heat from the
indoor air passing over the finned surface. Heat from the indoor air, causes the low pressure liquid to
evaporate, and cools the indoor air. The refrigerant is now a cool vapor.
• Refrigerant vapor passes through the insulated vapor line. If the unit is a heat pump, a reversing valve
will direct refrigerant into the accumulator. The accumulator controls liquid refrigerant and refrigerant
oil flow back to the compressor. Refrigerant vapor passes through the suction line to the compressor.
The cycle then repeats.
Figure 39 - Cooling Cycle
