Daikin MKS-T Series Service Manual page 91

SiSG121917E
4.10.6 High Discharge Pipe Temperature Control
When the compressor is operating, if the discharge pipe temperature exceeds a certain value,
the electronic expansion valve opens and the refrigerant runs to the low pressure side.
This procedure lowers the discharge pipe temperature.
4.10.7 Discharge Pipe Thermistor Disconnection Control
Outline
The disconnection of the discharge pipe thermistor is detected by comparing the discharge pipe
temperature with the condensing temperature. If the discharge pipe thermistor is disconnected,
the electronic expansion valve opens according to the outdoor temperature and the operation
frequency, operates for a specified time, and then stops.
After 3 minutes, the operation restarts and checks if the discharge pipe thermistor is
disconnected. If the discharge pipe thermistor is disconnected, the system stops after operating
for a specified time.
If the disconnection is detected repeatedly, the system is shut down. When the compressor runs
for 60 minutes without any error, the error counter is reset.
Details
Determining thermistor disconnection
When the starting control (30 seconds) finishes and the following condition is fulfilled, the
discharge pipe thermistor disconnection is ascertained.
Discharge pipe temperature + 6°C < outdoor heat exchanger temperature
When the thermistor is disconnected
When the disconnection is ascertained, the compressor continues operation for 9 minutes and
then stops.
If the compressor stops repeatedly, the system is shut down.
4.10.8 Gas Pipe Isothermal Control During Cooling
When the units are operating in multiple rooms, the gas pipe temperature is detected and the
electronic expansion valve opening is adjusted so that the temperature of the gas pipe in each
room becomes equal.
 When the gas pipe temperature > the average gas pipe temperature,
 When the gas pipe temperature < the average gas pipe temperature,
The temperatures are monitored every 40 seconds.
4.10.9 Target Discharge Pipe Temperature Control
The target discharge pipe temperature is obtained from the indoor and outdoor heat exchanger
temperature, and the electronic expansion valve opening is adjusted so that the actual
discharge pipe temperature becomes close to the target discharge pipe temperature. (Indirect
SH (superheating) control using the discharge pipe temperature)
The electronic expansion valve opening and the target discharge pipe temperature are adjusted
every 20 seconds. The opening degree of the electronic expansion valve is adjusted by the
followings.
 Target discharge pipe temperature
 Actual discharge pipe temperature
 Previous discharge pipe temperature
Part 4 Functions and Control
 the opening degree of electronic expansion valve in the corresponding room increases.
 the opening degree of electronic expansion valve in the corresponding room decreases.
SC
(Subcooling)
The target discharge pipe
temperature is set as to become
the target SH.
The inclination does not change
depending on the operating condition.
SH
(Superheating)
Control Specification
(R22539)
86