Daikin REYQ72, Serveice Manual

Page: 56 / 273

SiUS39-602 Basic Control
Function 45
2.3 Electronic Expansion Valve PI Control
Main Motorized Valve EV1 Control, Sub Motorized Valve EV2 Control
Carries out the motorized valve (Y1E, Y2E) PI control to maintain the evaporator outlet
superheated degree (SH) at constant during heating operation to make maximum use of the
outdoor unit heat exchanger (evaporator).
The optimum initial value of the evaporator outlet superheated degree is 9°F, but varies
depending on the discharge pipe superheated degree of inverter compressor.
Sub-cooling Motorized Valve EV3 Control
Makes PI control of the motorized valve (Y3E) to keep the superheated degree of the outlet gas
pipe on the evaporator side for the full use of the sub-cooling heat exchanger.
SH = Ts - Te SH : Evaporator outlet superheated degree (°F)
Ts : Suction pipe temperature detected by thermistor
R2T (°F)
Te : Low pressure equivalent saturation temperature
(°F)
SH = Tsh -Te SH : Outlet superheated degree of evaporator (
°
F)
Tsh : Suction pipe temperature detected with the
thermistor R5T (
°
F)
Te : Low pressure equivalent saturation temperature
(
°
F)