Daikin DP14CM Installation Manual

9
HEAT PUMP OPERATION
COOLING CYCLE
When the heat pump is in the cooling cycle, it operates exactly as a Sum-
mer 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 ap-
ply on the heating cycle except that “condenser” becomes “evaporator”,
“evaporator” becomes “condenser”, “cooling” becomes “heating”.
HEATING CYCLE
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 (condenser in the
cooling cycle) where the liquid is evaporated, and the vapor goes to the
compressor.
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 dis-
tributors also act as check valves to allow for the reverse of refrigerant
flow.
When the heat pump is in the heating cycle, the outdoor coil is function-
ing 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 tem-
perature and the outdoor coil temperature, the greater the heating ca-
pacity of the heat pump. This phenomenon is a characteristic 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 compressor, or refrigerant leak, etc.
Since the temperature of the refrigerant in the outdoor coil on the heat-
ing 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 accu-
mulation. 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.
DEFROST CONTROL
During operation the power to the circuit board is controlled by a tem-
perature 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. Accumula-
tion 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 remains closed. When the sensor opens (approxi-
mately 75° F), the defrost cycle is terminated and the timing period is
reset. If the defrost cycle is not terminated due to the sensor tempera-
ture, 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.