Daikin RZQ Series FCQ20EVA Service Manual page 172

Troubleshooting by Remote Controller
CHECK 12
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
(1) As suction superheated 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 air temperature, resulting that
cooling capacity becomes unavailable.
(4) If refrigerant shortage worsens, the electronic expansion valve remains fully open and suction
superheated 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
(∗1)
Low pressure
(∗2)
Suction superheated degree
Compressor frequency
Electronic expansion valve
Adequate level
3 This measured temperature is used to calculate the equivalent saturation pressure of the refrigerant.
(Refer to P.165.)
163
As compressor frequency
decreases, high pressure
decreases.
(Maintains a certain level
of low pressure)
As the electronic expansion valve
opening degree reaches the maximum,
suction superheated degree increases.
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)
Abnormal refri g erant shortage
Refrigerant shortage warning
Actual high pressure
When the refrigerant flow rate
decrease, it is impossible to
maintain a low pressure.
Reaches the lowest frequency
Inadequate level
SiME281501E
Cooling
Model RZQ
1
Intermediate heat
High exchanger thermistor
Pressure (3)
2
Pressure sensor
Low
Pressure
Service Diagnosis