Service manual

16
SYSTEM OPERATION
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
reversing valve is energized in the cooling mode not in the
heating mode as some previous models were.
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 expan-
sion device.
COOLING CYCLE
All Models
When the contacts of the room thermostat close making
terminals 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, indoor blower mo-
tor. 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 compressor and outdoor fan motor. This also ener-
gizes the indoor blower relay (control board) through the
room thermostat, 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 resistance heaters.
If electric heaters should be used, they may be controlled
by outdoor thermostats. (ATK01)
NOTE: Refer to the specifications section for the maxi-
mum heaters that may be installed for a specific unit.
COOLING
The refrigerant used in the system is R-22. It is clear, col-
orless, non-toxic, non-irritating, and non-explosive liquid.
The chemical formula is CHCLF
2
. The boiling point, at at-
mospheric pressure is -41.4°F.
A few of the important principles that make the refrigera-
tion cycle possible are: heat always flows from a warmer to
a cooler body, under lower pressure a refrigerant will ab-
sorb heat and vaporize at a low temperature, the vapors
may be drawn off and condensed at a higher pressure and
temperature to be used again.
The indoor evaporator coil functions to cool and dehumidify
the air conditioned spaces through the evaporative process
taking place within the coil tubes.
NOTE: The pressures and temperatures shown are for
demonstration purposes only. Actual temperatures and
pressures 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 remov-
ing heat from the refrigerant. As the refrigerant is cooled
below its condensing 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 outdoor 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
pressure 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 neces-
sary for the refrigerant to vaporize. Maintaining proper su-
perheat assures that liquid refrigerant is not returning to
the compressor which can lead to early compressor fail-
ure.
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 accumula-
tor before returning to the compressor.