– 138 –
Oveload control is to decrease the speed of the compressor and reduce the load when the load on the air conditioner
increases to an overload state, in order to protect the compressor, electronic components and power breaker.
Overloads are judgement by comparing the DC current level and value.
Fig. 7-4 shows the overload control system configuration and Fig. 7-5 is a characteristic diagram of overload judgement
values. There are two judgement methods-external judgement which compares the externally set value with the DC current
values regardless of the rotation speed and internal judgement which compares the set value that varies according to the
rotation speed programmed in the microcomputer software with the DC current value.
The filter consisting of R245 and C217 removes high harmonic components from the voltage generated by the current
flowing to Detection resistor; R245 and C217 average the voltage. This voltage is then input to IC4 pin and amplified and
is supplied to microcomputer pin . The microcomputer compares this input with the internally set value, and if the input
exceeds the set value, it enters overload control status.
Fig. 7-7 shows the rotation speed control. When the voltage at pin of the microcomputer exceeds the set value,
the microcomputer decreases the rotation speed of the compressor and reduces the load regardless of the rotation speed
commanded by the indoor microcomputer.
Overload external judgement circuit
(2) Overload control circuit (OVL control circuit)
(R24)
Detection
resistor
DC current
DC current
To power module
negative - terminal
Voltage amp
circuit
Motor control
process
AX-8T11 microcomputer
A/D
converter
A/D
converter
Judgement OVL
with respect to
externally set
value
Judgement OVL
according to the rotation
speed
Selects data according
to the rotation speed and
DC voltage
OVL start current data
DC voltage
(internal judgement)
Rotation speed data
Rotation speed
Judgement value according to the rotation speed
(internal judgement value)
Fig. 7-4 Overload Control System Configuration
Fig. 7-5