GPH16M Service Manual

SYSTEM OPERATION
19
COOLING
The refrigerant used in the system is R-410A. It is a clear,
colorless, non-toxic and non-irritating liquid. R-410A is a 50:50
blend of R-32 and R-125. The boiling point at atmospheric
pressure is -62.9°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 conditioned spaces through the evaporative process
taking place within the coil tubes.
NOTE: Actual temperatures and pressures are to be obtained
from the expanded ratings in the Technical Information
Manual.
High temperature, high pressure vapor leaves the compres-
sor through the discharge line 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 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.
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 liquid. 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.
COOLING CYCLE
Cooling Mode
When the contacts of the room thermostat close, making
terminals R to Y1, R to O, and R to G, the low voltage circuit
to the contactor is completed starting the compressor and
outdoor fan motor. The indoor blower motor is energized at
the cool speed.
When the thermostat is satisfied, breaking the circuit be-
tween R to Y1 and R to G, the compressor and outdoor fan
motor will stop. The indoor blower will stop after the fan off
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
Heat Pump Mode
On a call for first stage heat, the contacts of the room ther-
mostat close. This energizes terminals R to Y1 and R to G,
the low voltage circuit to the contactor is completed starting
the compressor and outdoor fan motor. This also energizes
the indoor blower motor.
When the thermostat is satisfied, breaking the circuit be-
tween R to Y1 and R to G, the compressor and outdoor fan
motor will stop. The indoor blower will stop after the pro-
grammed off delay.
During first stage operation the stat calls for second stage
heat. This energizes terminals R to Y2. This powers voltage
to the compressor solenoid allowing the compressor to shift
to full capacity. When the thermostat is staisfied, breaking
the circuit between R to Y1, R to Y2 and R to G, the com-
pressor and outdoor fan motor will stop. The indoor blower
will stop after the programmed off delay on the motor.
When auxiliary electric heaters are used the Aux stage heat-
ing contacts in the room thermostat close, which would be
wired to W1 at the unit low voltage connections, this would
energize the coil(s) of the electric heat contactor(s)/se-
quencer(s). Contacts within the contactor(s)/Sequencer(s) will
close, bringing on the electric resistance heaters. If auxilary
electric heaters should be used, the may be controlled by
outdoor thermostats (OT18-60A or OT/EHR18-60A).
Emergency Heat Mode (Heat Pumps)
NOTE: The following only applies if the unit has an approved
electric heat kit installed for auxiliary heating.
With the thermostat set to the emergency heat position, R to
W2/E will be energized. This will energize the electric heat
contactor(s)/sequencer(s) and the motor. The electric heat
will be energized through the normally open contacts of the
electric heat contactor(s)/sequencer(s). The indoor blower will
be energized through W2/E from the thermostat.
DEFROST CYCLE
Package Heat Pumps
The defrosting of the outdoor coil is jointly controlled by the
defrost control board and the defrost thermostat.
Solid State Defrost Control
During operation the power to the circuit board is controlled
by a temperature sensor, which is clamped to a feeder tube
entering the outdoor coil. Defrost timing periods of 30, 60, or
90 minutes may be selected by setting the circuit board
jumper to 30, 60, or 90 respectively. Accumulation of time for
the timing period selected starts when the sensor closes
(approximately 34° F), and when the room thermostat calls
for heat. At the end of the timing period, the unit’s defrost
cycle will be initiated provided the sensor remains closed.
When the sensor opens (approximately 60° F), the defrost
cycle is terminated and the timing period is reset. If the de-
frost cycle is not terminated due to the sensor temperature,
a twelve minute override interrupts the unit’s defrost period.
A/GPH16[24-60]M41*