SiME281906E
Check
Part 6 Service Diagnosis
202
6.9 Refrigerant Shortage Check
CHECK 11
As criteria for judging whether refrigerant is shortage or not, refer to the following operating
conditions.
Cooling
1. As suction superheating degree increases due to refrigerant shortage, the electronic
expansion valve tends to open (opens fully) in order to avoid overheat operation.
2. In response to decreased evaporator capacity caused by refrigerant shortage, capacity is
controlled in the inverter in order to maintain low pressure, which results in a decrease in
frequency.
3. Because of items 1 and 2 above, the compressor frequency decreases despite a large
difference (large load) between temperature set by the remote controller and indoor suction
air temperature, resulting that cooling capacity becomes unavailable.
4. If refrigerant shortage worsens, the electronic expansion valve remains fully open and
suction superheating degree further increases. In addition, because the compressor
frequency drops to the level of the lowest frequency, low pressure cannot be maintained.
Cooling
Suction superheating degree
Compressor frequency
Electronic expansion valve
Adequate level
As compressor frequency
decreases, high pressure
decreases.
(Maintains a certain level
of low pressure)
Actual high
pressure
Control high
pressure
When the refrigerant flow rate
decrease, it is impossible to
maintain a low pressure.
As the electronic expansion valve
opening degree reaches the maximum,
suction superheating degree increases.
Reaches the lowest
frequency
Inadequate
In response to decreased evaporator capacity
caused by refrigerant shortage, capacity is
controlled in the inverter in order to maintain a low
pressure, which resulting in a decrease in frequency.
The maximum opening degree of the
electronic expansion valve (480 pulses)
Avoid overheat operation by
changing SH target value
(Degree of inadequate refrigerant)
High pressure
(Heat exchanger
middle thermistor
(for outdoor unit
thermistor))
Low pressure
(Pressure sensor)
Refrigerant shortage
warning
Abnormal
refrigerant shortage
