Daikin RXSQ24TAVJU, Service Manual

Page: 88 / 311

Outline of Control (Indoor Unit) SiUS331708EA
75 Functions and Control
6.9 Electronic Expansion Valve Control
Electronic expansion valves in indoor units have the functions of conducting superheated degree control in
cooling operation and subcooled degree control in heating operation. However, if the indoor units receive a
control command such as a protection control command or a special control command from the outdoor unit, the
units will give priority to the control command.
• Superheated degree control in cooling operation
This function is used to adjust the opening of the electronic expansion valve so that superheated degree (SH),
which is calculated from the detection temperature (Tg) of the gas pipe thermistor (R3T) and the detection
temperature (Tl) of the liquid temperature thermistor (R2T) of the indoor unit, will come close to a target
superheated degree (SHS).
At that time, correction to the superheated degree is made according to the differences (
∆
T) between set
temperature and suction air temperature.
• Normally 5°C (9°F).
• As
∆
T (Remote controller set temp. – Suction air temp.) becomes larger, SHS becomes lower.
• As
∆
T (Remote controller set temp. – Suction air temp.) becomes lower, SHS becomes larger.
• Subcooled degree control in heating operation
This function is used to adjust the opening of the electronic expansion valve so that the high pressure equivalent
saturated temperature (Tc), which is converted from the detected pressure of the high pressure sensor in the
outdoor unit, and the subcooled degree (SC), which is calculated from the detected temperature (Tl) of the liquid
temperature thermistor (R2T) in the indoor unit, will come close to the target subcooled degree (SCS).
At that time, corrections to the subcooled degree are made according to differences (
∆
T) between set
temperature and suction air temperatures.
• Normally 5°C (9°F).
• As
∆
T (Remote controller set temp. – Suction air temp.) becomes larger, SCS becomes lower.
• As
∆
T (Remote controller set temp. – Suction air temp.) becomes lower, SCS becomes larger.
SH = Tg – Tl SH: Evaporator outlet superheated degree
Tg: Indoor unit gas pipe temperature (R3T)
Tl: Indoor unit liquid pipe temperature (R2T)
SHS (Target SH value) SHS: Target superheated degree
SC = Tc – Tl SC: Condenser outlet subcooled degree
Tc: High pressure equivalent saturated temperature
detected by the high pressure sensor (S1NPH)
Tl: Indoor unit liquid pipe temperature (R2T)
SCS (Target SC value) SCS: Target subcooled degree