Daikin RZQG71~140L7V1B Service Manual page 263

CHECK 11
Check for Inadequate Refrigerant
As criteria for judging whether refrigerant is inadequate or not, refer to the following operating conditions.
<Diagnosis of inadequate refrigerant>
In cooling operation
(1) As suction superheat 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 (1) and (2) above, the compressor frequency decreases despite a large difference (large load)
between temperature set by the remote controller and indoor suction temperature, resulting that cooling
capacity becomes unavailable.
(4) If refrigerant shortage worsens, the electronic expansion valve remains fully open and suction superheat
degree further increases. In addition, because the compressor frequency drops to the level of the lowest
frequency (52 Hz) and the refrigerant flow rate decrease, low pressure cannot be maintained.
Cooling
High pressure
Low pressure
Suction superheat degree
Compressor frequency
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.
Electronic expansion valve
Adequate level
Cooling
1
High Pressure
2
Low Pressure
3 This measured temperature is used to calculate the equivalent saturation pressure of the
252
(∗1)
As compressor frequency
decreases, high pressure
decreases.
(Maintains a certain
level of low pressure)
(∗2)
As the electronic expansion valve
opening degree reaches the maximum,
suction superheat degree increases.
Avoid overheat operation by
changing SH target value
(Degree of inadequate refrigerant)
Intermediate heat
exchanger
thermistor (3)
Pressure sensor
refrigerant.
(Refer to P.260.)
Refrigerant
shortage warning
When the refrigerant flow rate
decrease, it is impossible to
maintain a low pressure.
The maximum opening degree of the
electronic expansion valve (480 pulses)
Abnormal refrigerant
shortage
Actual high
pressure
Reaches the lowest frequency
Inadequate
Service Diagnosis
ESIE12-06