Daikin ZQG71~140L7V1B Service Manual page 216

Troubleshooting by Remote Controller
<Diagnosis of inadequate refrigerant>
In heating operation
(1) As suction superheat degree increases due to refrigerant shortage, the electronic expansion valve tends
to open (opens fully) to avoid overheat operation.
(2) As suction superheat degree increases due to refrigerant shortage, compressor frequency decreases
because suction superheat degree is controlled in order to prevent oil to the outdoor 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 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 temperature).
Heating
High pressure
Low pressure
Suction superheat degree
Compressor frequency
Electronic expansion valve
Heating
1
High Pressure
2
Low Pressure
3 This measured temperature is used to calculate the equivalent saturation pressure of the
204
(Maintains a certain
level of high pressure)
(∗1)
Indoor heat exchanger
temperature (Th2)
Indoor suction
temperature (Th1)
(∗2)
Suction superheat degree increases.
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.
Adequate level
Pressure sensor
Intermediate heat
exchanger
thermistor (3)
refrigerant.
(Refer to P.210.)
Refrigerant shortage warning
As compressor frequency
decreases, high pressure decreases.
A decrease in evaporator
capacity frequently puts the
system in defrost operation.
When frequency drops to the
lowest, a decrease in low
pressure becomes larger.
Drooping control by suction superheat degree
(Prevention of oil to heat exchanger from being
retained)
The maximum opening degree of the
electronic expansion valve (480 pulses)
Electronic expansion valve control
by avoiding superheat operation
(Degree of inadequate refrigerant)
ESIE12-06
Abnormal refrigerant shortage
Reaches the lowest frequency
Inadequate
Service Diagnosis