Daikin E Series Service Manual page 88

SiBE04-624
3.14.4 Target Discharge Pipe Temperature Control
Outline Superheat (SH) is required to insure that only gas and not liquid is sucked up by the
compressor. Because of the direct link between the SH and the discharge temperature (see Fig.
target discharge temperature), a control on the discharge temperature was made to be one of
the main control systems of Daikin air-conditioners. The discharge temperature and SH are
regulated by the expansion valve.
Fig.: Target discharge pipe temperature control graph
Detail The adjustment to the expansion valve opening is determined by the difference between the
actual discharge temperature and the target discharge temperature.
Starting conditions for this operation are:
Target discharge temperature = α cond. temp. - β evap. temp. + γ
α,β,γ ; predetermined constants related to different model types.
Discharge temp > target discharge temp, exp. valve will open.
Discharge temp < target discharge temp, exp. valve will close.
The target superheat (SH) will be 5°C ~ 7°C in cooling operation and 0°C in heating operation.
The discharge superheat always have to be larger then 10°C. Otherwise the unit will have liquid
compression. (depends on compressor type)
Function and Control
SC
The starting control and the 'operation room change' control (only for multi system) are
inactive.
The frequency changing control, high discharge temperature control and disconnected
discharge thermistor control are inactive
The defrost operation is inactive
The compressor is active
Discharge temp.
Incline depends
on compressor
and not on
operation
SH
Control Specification
(R5918)
77