Haier MRV 5-RC VP1-112B Service Manual page 169

3.2 Fan control
Control of MRV5-RC series DC motor
The air supply speed of outdoor unit can be set from speed 0 to 24 in accordance with the operating mode.
The operating is commonly at speed 1 - 24, and it is CVT (Continuously Variable Transmission) control between
speed 1 and 21.
3.3 4-way valve reversing
When the four-way valve is switched, the high pressure point of the valve needs to reach the minimum pressure
difference required by the valve action.
3.4 Pressure control
3.4.1 High pressure control in cooling
(1) High pressure setting value: 2.2MPa.
(2) When the pressure of the high pressure is lower than 2.2MPa, the outdoor fan rotates at a high pressure of
2.2MPa for fuzzy control.
3.4.2 Low pressure control in heating
(1) Control the low-pressure pressure during heating, in order to improve the stability of the system and the
reliability of the compressor.
(2) low pressure control in heating
• Low pressure control in heating is controlled by adjusting of the outdoor unit LEVa 1,2
3.5 Supercooling coil control
In cooling, the liquid outlet temperature Tliqsc of the suppercooling coil is controlled by adjusting the electronic
expansion valve LEVb.
Ordinary high drop, improve system operation efficiency by obtaining a certain degree of supercooling.
3.6 Defrosting control
When any outdoor unit meets the defrost entry condition, it will switch the four-way valve to start defrosting.
3.7 Oil return in heating
During oil return in heating, the four-way valve is switched to the cooling state and the indoor units are anti-cold air
control in the whole process
3.8 Compressor bottom temperature control
(1) When the temperature at the bottom of the compressor increases, the liquid bypass cooling is performed by
opening the corresponding SV31,2.
(2) Before the compressor is started, the bottom of the compressor is heated by heater so that the internal liquid
refrigerant evaporates sufficiently before the compressor is started to avoid excessive dilution of the compressor oil.
3.9 Compressor top temperature (Td1/Td2) control
(1) When the temperature at the top of the compressor rises, the liquid bypass cooling is performed by opening the
corresponding SV31,2.
(2) When the temperature at the top of the compressor rises to 115°C, the output frequency of the compressor is
limited.
3.10 High pressure protection control in heating
In heating, the high pressure is detected by the high pressure ensors Pd1, Pd2 of each compressor so as to control
the compressor capacity to avoid high pressure rise.
3.11 Current safety control
(1) If the compressor current exceeds the specified upper limit, reducing the operating frequency for control before
the current becomes the exit value.
(2) Even if the current dropped to the minimum speed cannot reach the upper limit value, the operation stops.
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