1.7 REFRIGERANT CYCLE -- HEAT PUMP
DISCHARGE |
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LIQUID |
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SUCTION |
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STRAINER
REVERSING VALVE
ACCUMULATOR
COMPRESSOR
OUTDOOR COIL
Figure 1-9 Refrigerant Flow Schematic -- Heat Pump -- (Cool Mode)
1.7.1 Cooling
The cooling cycle is energized when the thermostat, located in the ceiling unit, calls for cooling The system controls are positioned for “normal” refrigerant flow, with the compressor discharge delivered to the outdoor coil and liquid delivered to the indoor coil. (See Figure
The main components of the system are the compressor, reversing valve,
The compressor raises the pressure and the temperature of the refrigerant and forces it through the discharge line and reversing valve into the outdoor coil.
The outdoor fan circulates surrounding air (which is at a temperature lower than the refrigerant) over the outside of the coil tubes. Heat transfer is established from the refrigerant (inside the tubes) to the outdoor air (flowing over the tubes). The tubes have fins designed to improve the transfer of heat from the refrigerant gas to the air; this removal of heat causes the refrigerant to liquefy, thus liquid refrigerant leaves the coil and flows through the strainer to the capillary tube. The strainer removes any impurities within the refrigerant system.
The capillary tube meters the flow of liquid refrigerant to the indoor coil. As the refrigerant flows through the
capillary tube, there is a reduction in pressure and temperature.
The indoor blower (fan) pulls inside air through the filters, which remove particulate matter, and then pass the cleaned air through the indoor coil.
The low pressure, low temperature liquid that flows into the indoor coil tubes is colder than the air that is circulated over the tubes. Heat transfer is established from the indoor air (flowing over the tubes) to the refrigerant (flowing inside the tubes). The indoor coil tubes have aluminum fins to increase heat transfer from the air to the refrigerant; therefore the cooler air is circulated to the interior of the vehicle.
The transfer of heat from the air to the low temperature liquid refrigerant in the indoor coil causes the liquid to vaporize. This low temperature, low pressure vapor passes into the accumulator. The accumulator is designed with the inlet tube delivering refrigerant to the bottom of the tank and the outlet tube taking refrigerant form the top of the tank. This arrangement ensures that only vapor refrigerant is returned to the compressor, where the cycle repeats.
When ventilation only is selected, the indoor fan functions to circulate air throughout the vehicle. The refrigerant cycle will remain off.