Panasonic CS-VZ9SKE Service Manual page 128

17.4.27 F91 (Refrigeration Cycle Error)
Troubleshooting
Check if the 2- and 3-way valves are open.
Check for the characteristics of the indoor unit heat exchanger temperature sensor.
Refer to the characteristic table for electronic circuit diagram.
(Remove the connector and check the resistance value of the sensor.)
Normal
Check the gas pressure during the rated cooling operation.
Gas pressure is high or low?
Check for presence of gas leak.
Diagnosis Procedures and Cause
Yes
For some models, the sensor is not connected by a connector
but it is directly soldered to the board.
In this case, replace the control board.
Abnormal
Low
There is a gas leak
No
Abnormal
Normal
High
There is no
gas leak
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Measures to be Taken
Open the 2- and 3-way valves.
Replace the indoor unit heat
exchanger temperature sensor.
Replace the outdoor unit control board.
Replace the compressor.
Replace the capillary tube or
expansion valve.
Replace the part from which gas is
leaking.