Daikin DCC Series, Installation Instructions Manual

13

listed at low load conditions and low ambient condensing 

temperatures. Values in Appendix B can slightly exceed at 

high load conditions and high ambient condensing tempera-

tures.

HEAT PUMP OPERATION

C

OOling

 C

yCle

When the heat pump is in the cooling cycle, it operates ex-

actly 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 “evapora-

tor”, “evaporator” becomes “condenser”, “cooling” becomes 

“heating”.

h

eating

 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  through the reversing 

valve. Hot discharge vapor from the compressor is directed 

to the indoor coil (evaporator on 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 on the cooling cycle) where the liquid is evapo-

rated, 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 on 

the cooling cycle and the heating cycle.  In addition to a 

reversing valve, a heat pump is equipped with an expan-

sion 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 per

-

form the same function on the heating cycle as on the 

cooling cycle.  The flowrator distributors also act as check 

valves to allow for the reverse of refrigerant flow.

When the heat pump is on the heating cycle, the outdoor 

coil is functioning as an evaporator.  The temperature of the 

refrigerant in the outdoor coil must be below the tempera-

ture 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 char-

acteristic 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 compo-

nent 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 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 refrig

-

erant to provide hot gas in the outdoor coil to melt the frost 

accumulation. 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.

d

efrOst

 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 connecting 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 remains 

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 tem-

perature, a ten minute override interrupts the unit’s defrost 

period.