Installation Manual

9
HEAT PUMP OPERATION
COOLING CYCLE
When the heat pump is in the cooling cycle, it operates exactly as a
Summer Air Conditioner unit. In this mode, all the charts and data for
service that apply to summer air conditioning apply to the heat pump.
Most apply on the heating cycle except that “condenser” becomes
“evaporator”, “evaporator” becomes “condenser”, “cooling” becomes
“heating”.
HEATING C YCLE
The heat pump operates in the heating cycle by redirecting refrigerant
flow through the refrigerant circuit external to the compressor. This is
accomplished with the reversing valve. Hot discharge vapor from the
compressor is directed to the indoor coil (evaporator in the cooling
cycle) where the heat is removed, and the vapor condenses to liquid.
It then goes through the expansion device to the outdoor coil (con-
denser in the cooling cycle) where the liquid is evaporated, and the
vapor goes to the compressor.
E
V
A
P
O
R
A
T
O
R
COOLING
SERVICE VALVE
SERVICE PORT
REVERSING VALVE
C
O
N
D
E
N
S
E
R
SERVICE PORT
COMPRESSOR
SERVICE PORT
ACCUMULATOR
EXPANSION DEVICE
CHECK VALVE
ORIFICE
SERVICE
VALVE
CHECK VALVE
ORIFICE
INDO OR
COIL
DISTRIBUTOR
OUTDOOR
COIL
E
V
A
P
O
R
A
T
O
R
HEATING
SERVICE VALVE
SERVICE PORT
REVERSING VALVE
C
O
N
D
E
N
S
E
R
COMPRESSOR
SERVICE PORT
ACCUMULATOR
CHECK VALVE
ORIFICE
SERVICE
VALVE
CHECK VALVE
ORIFICE
INDOOR
COIL
DISTRIBUTOR
OUTDOOR
COIL
DISTRIBUTOR
When the solenoid valve coil is operated either from heating to cooling
or vice versa, the piston in the reversing valve to the low pressure
(high pressure) reverse positions in the reversing valve.
The following figures show a schematic of a heat pump in the
cooling cycle and the heating cycle. In addition to a reversing valve,
a heat pump is equipped with an expansion device and check
valve for the indoor coil, and similar equipment for the outdoor coil.
It is also provided with a defrost control system.
The expansion devices are flowrator distributors and perform the
same function in the heating cycle as in the cooling cycle. The
flowrator distributors also act as check valves to allow for the re-
verse of refrigerant flow.
When the heat pump is in the heating cycle, the outdoor coil is func-
tioning as an evaporator. The temperature of the refrigerant in the
outdoor coil must be below the temperature of the outdoor air in order
to extract heat from the air. Thus, the greater the difference in the
outdoor temperature and the outdoor coil temperature, the greater the
heating capacity of the heat pump. This phenomenon is a character-
istic of a heat pump. It is a good practice to provide supplementary
heat for all heat pump installations in areas where the temperature
drops below 45° F. It is also a good practice to provide sufficient
supplementary heat to handle the entire heating requirement should
there be a component failure of the heat pump, such as a compres-
sor, or refrigerant leak, etc.
Since the temperature of the refrigerant in the outdoor coil on the
heating cycle is generally below 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 refrigerant to provide hot gas in the outdoor
coil to melt the frost accumulation. This is accomplished by re-
versing 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 energized.
DEFROST C ONTROL
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 and 90 minutes
may be selected by setting the circuit board jumper to 30, 60 and
90 respectively. Accumulation of time for the timing period selected
starts when the sensor closes (approximately 31° F), and when
the wall thermostat calls for heat. At the end of the timing period,
the unit’s defrost cycle will be initiated provided the sensor re-
mains closed. When the sensor opens (approximately 75° F), the
defrost cycle is terminated and the timing period is reset. If the
defrost cycle is not terminated due to the sensor temperature, a
twelve minute override interrupts the unit’s defrost period.
SUGGESTED FIELD TESTING/TROUBLE SHOOTING
1. Run unit in the heating mode (room thermostat calling for
heat).
2. Check unit for proper charge. Note: Bands of frost on the
condenser coil indicate low refrigerant charge.
3. Shut off power to unit.
4. Disconnect outdoor fan by removing the outdoor fan motor
wire from “DF2” on defrost control.
5. Restart unit and allow frost to accumulate.
6. After a few minutes of operation, the unit’s defrost
thermostat should close. To verify this, check for 24 volts
between “DFT” and “C” on board. If the temperature at the
thermostat is less than 28° F and the thermostat is open,
replace the unit’s defrost thermostat, as it is defective.
7. When the unit’s defrost thermostat has closed, short the
test pins on the defrost board until the reversing valve
shifts, indicating defrost. This should take up to 22
seconds depending on what timing period the control is
set on. After defrost initiation, the short must instantly be
removed or the unit’s defrost period will only last 3
seconds.