Goodman GSX Series Installation & Operation Instructions page 10

I. Shut off power to unit.
J. Replace outdoor fan motor lead and turn on power.
OPERATION - GENERAL
EXPLANATION AND GUIDANCE
The heat pump is a relatively simple device. It operates exactly
as a Summer Air Conditioning unit when it is on the cooling
cycle. Therefore, all the charts and data for service that apply to
summer air conditioning apply to the heat pump when it is on
the cooling cycle, and most apply on the heating cycle except
that "condenser" becomes "evaporator", "evaporator" becomes
"condenser" and "cooling" becomes "heating".
When the heat pump is on the heating cycle, it is necessary
to redirect the refrigerant flow through the refrigerant circuit
external to the compressor. This is accomplished with a
reversing valve. Thus, the hot discharge vapor from the
compressor is directed to the inside coil (evaporator on the
cooling cycle) where the heat is removed, and the vapor
condenses into liquid. It then goes through a capillary tube, or
expansion valve, to the outside coil (condenser on the cooling
cycle) where the liquid is evaporated, and vapor goes to the
compressor.
When the solenoid valve is operated either from heating to
cooling or vice versa, it moves the pilot valve, thus putting
suction pressure (low pressure) on one side of the piston of
the reversing valve, and since discharge pressure (high pres-
sure) is on the other side of the piston, the piston slides to the
low pressure side and reverses the flow of the refrigerant in
the circuit.
The following figures show a schematic of a heat pump on
the cooling cycle and the heating cycle.
Heat Pump Refrigerant Circuit
In addition to a reversing valve, a heat pump is equipped
with an expansion device and check valve for the inside coil,
and similar equipment for the outside coil. It is also provided
with a defrost control system.
The expansion device performs the same function on the
heating cycle as on the cooling cycle. The check valves are
required due to the reverse flow of refrigerant when chang-
ing from cooling to heating or vice versa.
When the heat pump is on the heating cycle, at which time
the outdoor coil is functioning as an evaporator, the tempera-
ture of the refrigerant in the outdoor coil must be below the
temperature of the outdoor air in order for the refrigerant in
the outdoor coil to extract heat from the air. Thus, the greater
the difference in outdoor temperature and outdoor coil
temperature, the greater the heating capacity of the heat
pump. Since this is characteristic of heat pumps, it is good
practice to provide supplementary heat for all heat pump
installations in areas where the temperature drops below
7.2°C. It is also good practice to provide sufficient supple-
mentary heat to handle the entire heating requirements if
there should be a failure of heat pump, such as a compressor
failure, or refrigerant leak, etc.
Since the temperature of the liquid refrigerant in the outdoor coil
on the heating cycle is generally below the freezing point, frost
forms on the surfaces of the outdoor coil under certain
weather conditions of temperature and relative humidity,
Therefore, it is necessary to reverse the flow of the refriger-
ant to provide hot gas in the outdoor coil to melt the frost
accumulation. This is accomplished by reversing the heat
pump to the cooling cycle. At the same time, the outdoor fan
stops to hasten the temperature rise of the outdoor coil and
lessen the time required for defrosting. The indoor blower
continues to run and the supplementary heaters are ener-
gized.
SERVICE:
The following information is for use by qualified service
agency only; others should service this equipment.
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