Control Of Electronic Expansion Valve - Daikin RXYQ96PYDN Service Manual

SiUS34-801A_b

6. Control of Electronic Expansion Valve

Electronic expansion valves in indoor units conduct superheated degree control in cooling
operation and subcooled degree control in heating operation. If the indoor units receive any 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 (T1) 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 (
between set temperature and suction air thermistor temperature.
• 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 (T1) 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 (
set temperature and suction air thermistor temperatures.
Indoor Unit
SH = Tg - T1
SHS (Target SH value)
• Normally 41°F.
Δ
• As T (Remote controller set temp. - return air temp.) becomes larger, SHS becomes
lower.
Δ
• As T (Remote controller set temp. - return air temp.) becomes smaller, SHS becomes
higher.
SC = Tc - T1
SCS (Target SC value)
• Normally 41°F.
Δ
• As T (Remote controller set temp. - return temp.) becomes larger, SCS becomes lower.
Δ
• As T (Remote controller set temp. - return temp.) becomes lower, SCS becomes larger.
SH: Evaporator outlet superheated degree (°F)
Tg: Indoor unit gas pipe temperature (R3T)
T1: Indoor unit liquid pipe temperature (R2T)
SHS: Target superheated degree
SC: Condenser outlet subcooled degree (°F)
Tc: High pressure equivalent saturated temperature
detected by the high pressure sensor (S1NPH)
T1: Indoor unit liquid pipe temperature (R2T)
SCS: Target subcooled degree
Control of Electronic Expansion Valve
Δ
T)
Δ
T) between
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