24
SYSTEM OPERATION
The restrictor orifice or check valve at the indoor coil will open
by the flow of refrigerant letting the now condensed liquid
refrigerant bypass the indoor expansion device. The orifice
or check valve at the outdoor coil will be forced closed by the
refrigerant flow, thereby utilizing the outdoor expansion de-
vice.
COOLING CYCLE
All Models
When the contacts of the room thermostat close making ter-
minals R to Y & to G, on the control board. Heat pumps
thermostat make the R to O terminals also.
The control board recognizes this as a demand for cooling
and energizes the compressor contactor and indoor blower
motor. The blower delay is an integral part of the control board.
When the thermostat is satisfied, it opens its contacts, break-
ing the low voltage circuit, causing the compressor contactor
to open and indoor fan to stop after a 30 second delay.
If the room thermostat fan selector switch should be set to
the "on" position then the indoor blower would run continu-
ous rather than cycling with the compressor.
HEATING CYCLE
Package Heat Pumps
When the thermostat calls for heat, making terminals R to Y,
the low voltage circuit of the transformer is completed. The
control board applies power to the contactor starting the com-
pressor and outdoor fan motor. This also energizes the in-
door blower relay (control board) through the room thermo-
stat, starting the indoor blower motor.
When auxiliary electric heaters are used, a two stage heat-
ing single stage cooling thermostat would be installed.
Should the second stage heating contacts in the room ther-
mostat close, which would be wired to W at the unit control
board, this would energize the coil of the electric heat relay(s).
Contacts within the relay(s) will close, bringing on the resis-
tance heaters.
If electric heaters should be used, they may be controlled by
outdoor thermostats. (ATK01)
NOTE: Refer to the specifications section for the maximum
heaters that may be installed for a specific unit.
DEFROST CYCLE
Package Heat Pumps
The defrosting of the outdoor coil is jointly controlled by the
defrost control board, defrost (30/60) control and compressor
run time.
Solid State Timer
The defrost timer board can be connected for one of three (3)
time intervals. 30 minutes, 60 minutes, and 90 minutes (Fac-
tory connected @ 60 min.). Package heat pumps manufac-
tured after May 1999 (9905 Serial date code) will be factory
set @ 30 min.
COOLING
The refrigerant used in the system is R-22. It is clear, color-
less, non-toxic, non-irritating, and non-explosive liquid. The
chemical formula is CHCLF
2
. The boiling point, at atmospheric
pressure is -41.4°F.
A few of the important principles that make the refrigeration
cycle possible are: heat always flows from a warmer to a
cooler body, under lower pressure a refrigerant will absorb
heat and vaporize at a low temperature, the vapors may be
drawn off and condensed at a higher pressure and tempera-
ture to be used again.
The indoor evaporator coil functions to cool and dehumidify
the air through the evaporative process taking place within
the coil tubes.
NOTE:
The pressures and temperatures shown are for dem-
onstration purposes only. Actual temperatures and pres-
sures are to be obtained from the "Cooling Performance
Chart."
High temperature, high pressure vapor leaves the compres-
sor through the discharge line, through the reversing valve on
heat pump models, and enters the condenser coil. Air drawn
through the condenser coil by the condenser fan causes the
refrigerant to condense into a liquid by removing heat from
the refrigerant. As the refrigerant is cooled below its con-
densing temperature it becomes subcooled.
The subcooled high pressure liquid refrigerant now leaves the
condenser coil via the liquid line until it reaches the indoor
expansion device. (Heat pump models will also have an out-
door expansion valve/check valve assembly or a restrictor
orifice installed in the liquid line).
As the refrigerant passes through the expansion device and
into the evaporator coil a pressure drop is experienced caus-
ing the refrigerant to become a low pressure vapor. Low pres-
sure saturated refrigerant enters the evaporator coil where
heat is absorbed from the warm air drawn across the coil by
the evaporator blower. As the refrigerant passes through the
last tubes of the evaporator coil it becomes superheated,
that is, it absorbs more heat than is necessary for the refrig-
erant to vaporize. Maintaining proper superheat assures that
liquid refrigerant is not returning to the compressor which
can lead to early compressor failure.
Low pressure superheated vapor leaves the evaporator coil
and returns through the suction line to the compressor where
the cycle begins again. On heat pump models the refriger-
ant must travel through the reversing valve and accumulator
before returning to the compressor.
HEATING - Heat Pump Models
The heating portion of the refrigeration cycle is similar to the
cooling cycle. The reversing valve reverses the flow of the
refrigerant. The indoor coil now becomes the condenser coil
and the outdoor coil becomes the evaporator coil. The revers-
ing valve is energized in the cooling mode not in the heating
mode as some previous models were.
SYSTEM OPERATION
