2WAY VRF SYSTEM
Control Functions
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4. Special Control
2WAY VRF SYSTEM
Control Functions
9-1. Type of expansion valves
9-2. Power Initialization
MOV1 : For upper side heat exchanger
MOV2 : For lower side heat exchanger
If no indoor units have started (even once) after the power supply to the outdoor unit, the MOV holds the 480
pulses (fully open).
9-3. Control of expansion valves
Expansion valves for heat exchanger control according to the operation mode.
Cooling
Heating
Mode of system
Compressor
MOV1 (pulse)
MOV2 (pulse)
Stop
Stop
0
0
Operation
480
480
Stop
0
0
Operation
0 ~ 480
0 ~ 480
Stop
0
0
* When the indoor unit receives the signal for operation request from the control equipment, the pulse turns
other than the 480 pulses (regardless of the thermostat ON/OFF or operating ON/OFF).
It is necessary to switch ON the power supply again if the 480 pulses are required.
* If any one compressor in the outdoor unit is operating at heating mode, expansion valves perform SH
control.
SH control adjusts the difference of temperature between the liquid and gas temperature to
-1.8deg F ~ 9deg F (-1deg C ~ 5deg C).
(9) MOV for Heat Exchanger [MOV1, MOV2]
2WAY VRF SYSTEM
Control Functions
4. Special Control
(10) SC Circuit Expansion Valve [MOV4]
During cooling operation, the liquid refrigerant which condenses at the outdoor unit heat exchanger flows into
the receiver tank, and SC (sub-cooling) approaches 32°F (0°C).
When SC is small and the length of the tubing connecting the indoor and outdoor units is long, the refrigerant
flow in the indoor unit will be reduced significantly.
To prevent this trouble from occurring, MOV4 operates so as to increase super-cooling in the double tube coil.
10-1.
(11) Crankcase Heater Control [CH1, CH2]
When the compressor stops, the crankcase heater of its own compressor is turned ON in the following conditions.
Cooling SC Control
During heating operation, MOV4 operates so as to
improve the refrigerant flow of the outdoor unit heat
exchanger and the system.
MOV4 controls refrigerant flow volume so that it will
not flow back to the compressor in the liquid state.
MOV4 controls the difference of temperature
between the SCG thermistor and low pressure
saturated temperature to 5.4deg F (3deg C).
10-2. Heating SC Control
When the discharge temperature increases to
194°F (90°C) or more, MOV 4 opens to 100 pulses
to cool down the compressor.
Then, the MOV 4 operates according to the state of
the discharge temperature between 20 ~ 480 pulses.
This operation takes priority over SC control.
This operation is continued until discharge
temperature decreases to 176°F (80°C) or less.
10-3. Discharge Temperature Control of Compressor
MOV4 controls the difference of temperature between the SCG thermistor and low pressure saturated temperature
to 5.4deg F ~ 9deg F (3deg C ~ 5deg C).
Thermistor (SCG)
MOV4 (SH control)
Gas refrigerant
returns to accumulator.
Liquid refrigerant
Refrigerant on the inner side
evaporates, cooling the liquid
refrigerant on the outer side.
Liquid refrigerant
Thermistor (SCG)
MOV4 (Discharge temperature control of compressor)
Liquid refrigerant
returns to accumulator.
Liquid refrigerant
Does not fully evaporate,
resulting in liquid back-up.
Liquid refrigerant
When the discharge temperature ≤ the outdoor air tempe 27deg F (+15deg C)
When the outdoor air temperature ≤ 68°F (20°C)
When the compressor stops and 30 minutes later.
4. Output of PCB
SM830237-07_北米向け2WAY_VRF.indb 16
18/06/19 18:55:32