Daikin RZQ Series FCQ20EVA Service Manual page 173

SiME281501E
<Diagnosis of inadequate refrigerant>
In heating
(1) As suction superheated degree increases due to refrigerant shortage, the electronic expansion valve
tends to open (opens fully) to avoid overheat operation.
(2) As suction superheated degree increases due to refrigerant shortage, compressor frequency decreases
because suction superheated degree is controlled in order to prevent oil to the outdoor unit heat
exchanger from being retained.
(3) Because of (1) and (2) above, evaporator capacity and compressor frequency decrease despite a large
difference (large load) between temperature set by the remote controller and indoor suction air
temperature, resulting that high pressure cannot be maintained and heating capacity becomes
unavailable. Also a decrease in evaporator capacity frequently puts the system in defrost operation.
(4) If refrigerant shortage worsens, high pressure becomes smaller than saturated pressure equivalent to
indoor heat exchanger temperature (or indoor suction air temperature).
Heating
(Maintains a certain
level of high pressure)
High pressure
(∗1)
Low pressure
(∗2)
Suction superheated degree
Compressor frequency
In response to decreased evaporator capacity
caused by refrigerant shortage, capacity is
controlled in the inverter in order to maintain high
pressure, which resulting in a rise in 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.)
Service Diagnosis
Refrigerant shortage warning
As compressor frequency
decreases, high pressure
decreases.
Indoor heat exchanger temperature (Th2)
Indoor suction air temperature (Th1)
A decrease in evaporator capacity frequently
puts the system in defrost operation.
Suction superheated degree increases.
Drooping control by suction superheated
degree (Prevention of oil to heat exchanger
from being retained)
Electronic expansion valve control by avoiding superheated operation
(Degree of inadequate refrigerant)
Abnormal refrigerant shortage
When frequency drops to the
lowest, a decrease in low
pressure becomes larger.
Reaches the lowest frequency
The maximum opening degree of the
electronic expansion valve (480 pulses)
Inadequate
Troubleshooting by Remote Controller
Heating
Model RZQ
1
Pressure sensor
High
Pressure
2
Intermediate heat
Low exchanger thermistor
Pressure (3)
164