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17. CONTORL LOGIC DESCRIPTION
17. Control logic description
17.1 An illustration to outdoor unit signal
(1) Communication between indoor and outdoor units:
The communication between the outdoor unit, thermostat and the indoor unit is achieved
through 24V alternating current, as shown in figure below.
The thermostat controls the signal output of Y and B, and the outdoor unit identifies its
operation mode according to these two signals. If Y-C is high level, the outdoor unit starts in
cooling mode; if both Y-C and B-C are high level, the outdoor unit starts in heating mode.
When the outdoor unit meets its defrosting conditions in heating mode, W-C is high level,
and when it exits from defrosting function, W-C is low level.
Thermostat
Y
Y
C WW C
C W
B
B
Y：Compressor signal；
B：4-way valve signal；
W：Defrosting signal;
C：Common signal.
Indoor unit
Outdoor unit
17.2 Cooling Mode
(1) Start conditions:
When high level compressor signal and low level 4-way valve signal are received from the
thermostat, that is Y-C is high level and B-C is low level.
(2) Stopping operating：
① Stopping conditions:
When low level compressor signal is received from the thermostat, that is Y-C is low level.
② Actions:
The compressor keeps operating with its current frequency, and detects its system pressure at
the same time.
(a) If the pressure changes more than 0.04MPa【e2】in 10 seconds, the compressor stops
operating.
(b) If the pressure changes less than 0.04MPa【e2】in 10 seconds, the compressor keeps
operating and the target pressure is set to increase by 0.2MPa【e2】based on the current
system pressure. The motor and electronic expansion valve are controlled as usual, the
protection function and oil-return control are valid.
③ Stopping conditions:
When the compressor signal received from the thermostat is high level and 4-way valve signal
is low level, that is Y-C is high level and B-C is low level, the unit restores the normal target
pressure to operate or when the compressor has operated for 30min【e2】with the increased
target pressure, it is taken as it has stopped operating.
67
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