Unit Control
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high pressure side. Under the heating or water heating mode, the operating frequency of the fan is
adjusted according to the pressure at the low pressure side. During defrosting, the fan stops and
resumes operation when defrosting ends up.
2.7 Control to the 4-way Valve
The 4-way valve always keeps on under the cooling mode and will off after the compressor starts up
under the heating or water heating mode. When the unit comes into defrosting, the 4-way valve will be
on and resume the off status when defrosting ends up. For shutdown under the heating mode, the 4-way
valve will be closed after the compressor stops.
2.8 Control to the Water Pump
The water pump firstly will run at the initialized speed and then adjust the speed according to the
entering/leaving water temperature difference. When the temperature difference is large, the fan runs at
the high speed. When the temperature difference is small, the fan runs at the low speed.
2.9 Control the Electrostatic Expansion Valve
There are two electrostatic expansion valves for two-stage throttling control. The opening angle of
the first-stage electrostatic expansion valve is adjusted based on the ratio of readings of the
high-pressure sensor, low-pressure sensor and enthalpy-adding sensor. The opening angle of the
second-stage is adjusted based on the suction superheating degree.
2.10 Protection Control
(1) Compressor Low-pressure Protection
When it is detected continuously that pressure at the low side is too low, then low-pressure
protection will occur and this error will be displayed at the controller, all loads act as per the shutdown
sequence. This error is unrecoverable and can be cleared unless repowered on.
(2) High Discharge Temperature Protection
When it is detected continuously that the discharge temperature is higher than the recoverable
temperature, the electrostatic expansion valve will turn to the maximum opening angle with large step
until the discharge temperature is lower than the recoverable temperature. However, if this condition
remains, the compressor will restrict the frequency output or lower its frequency three times. At any time,
if it is detected that the discharge temperature is higher than the set point for protection for three
seconds, the compressor will stop and the unit comes into high discharge temperature protection.
(3) Refrigerant Loss Protection
When the unit receives the “On” demand (through On/Off key operation or automatic freeze
protection), it will immediately detect the temperature of the high-pressure sensor and the environment
temperature. If the temperature of the high-pressure sensor is lower than the set point, this error will be
displayed with the error indicating LED flashing. In this case, the unit is not allowed to start up unless this
error does not exit. Once the compressor starts up, the system will no longer detect refrigerant loss
protection.
(4) Water Pump Protection
When it is detected continuously for three seconds that the unit comes into water pump overload
protection, then all loads except the water pump of the solar system and the auxiliary electric heater of
the water tank will stop. Three minutes later, all loads resume normal operation. When it is detected
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