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 W
W
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.
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