Daikin FTX25JVEA9, Service Manual

Page: 139 / 410

System control Si18-201
126 Main Functions
3.11 Capacity Control
3.11.1 Outdoor Unit Motorized Valve Low Pressure (Cooling Capacity)
Control
Outline This functions forms a discharge-suction bypass circuit to prevent the suction pressure from
dropping (freezing of indoor unit) during cooling due to excessively low indoor heat exchange
capacity even when operating at the minimum frequency.
The freeze prevention status from the indoor unit is used to calculate target suction pressure
LPMK, and the discharge bypass motorized valve is controlled to achieve the target suction
pressure.
Details Zones are produced based on the freeze prevention status sent from the BP unit (indoor unit),
and the freeze prevention control provides cooling capacity control when the operating
frequency reaches the minimum frequency.
The cooling capacity control adjusts the EVP to vary the target low temperature based on the
freeze prevention status so the target low pressure is attained.
EVP (discharge bypass motorized valve) operating amount
The suction pressure is detected during each sampling operation (20 sec). The difference target
LP is used to determine the amount of valve operation.
In case of Target LP < Current LP, EVP: close
In case of Target LP > Current LP, EVP: open
The capacity control ends when 60 seconds elapse from the time the EVP closes fully.
Decrease in target LP : 0.025kg/cm²/20sec
Increase in target LP : 0.025kg/cm²/20sec
Reset zone
No-change zone
Drooping zone
(M1016)