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T--298
1-11
COMPRESSOR
ACCUMULATOR
REVERSING VALVE
INDOOR COIL
OUTDOOR COIL
STRAINER
CAPILLAR Y
TUBE
DISCHARGE
SUCTION
LIQUID
Figure 1-10 Refrigerant Flow Schematic -- Heat Pump -- (Heat Mode)
1.7.2 Heating
The heating cycle is energized when the thermostat,
located in the ceiling unit, calls for heat The system
controls are positioned for “reverse” refrigerant flow,
with the compressor discharge delivered to the indoor
coil and liquid delivered to the outdoor coil. (See
Figure 1-10.)
The main components of the system are the
compressor, r eversing valve, indoor coil, capillary tube,
strainer, air-cooled outdoor coil, and the accumulator.
The compressor raises the pressure and the
temperature of the r efrigerant and forces it through the
discharge line and reversing valve into the indoor coil.
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 vehicle a ir ( which is at a temperature lower than the
refrigerant) passes over the outside of the coil tubes.
Heat transfer is established from the refrigerant ( inside
the tubes) to the vehicle 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
outdoor coil. The strainer removes any impurities within
the refrigerant system.
The capillary tube meters the flow of liquid refrigerant to
the outdoor coil. As the refrigerant flows through the
capillary tube, there is a reduction in pressure and
temperature.
The low pressure, low temperature liquid that flows into
the outdoor coil tubes is colder than the outdoor air t hat
is circulated over the tubes. Heat transfer is established
from the outdoor air (flowing over the tubes) to the
refrigerant (flowing i nside the tubes). The outdoor coil
tubes have aluminum fins to increase heat transfer from
the air to the refrigerant.
The transfer o f heat from the air to the low temperature
liquid refrigerant in the outdoor c oil causes the liquid to
vaporize. This low temperature, low pressure vapor
passes into the accumulator. The accumulator is
designed wit h the inlet tube delivering refrigerant to t he
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.