F91 - Refrigerant cycle abnormality.
Panasonic lists F91 as a refrigerant cycle abnormality in the self-diagnosis table for inverter air conditioners.
Applied here to Wall-Mounted Standard Inverter R32 MPU multi-split models, but Panasonic says exact code support and interpretation can vary by operating instructions.
Severity
High
Display
Displayed as F91 by the self-diagnosis function on compatible Panasonic inverter air conditioners.
Support first?
Often not
Models in range
CS-MPU9YKZ, CS-MPU12YKZ, CS-MPU18YKZ
What to do first
Start with these checks
- 1Stop operation if cooling performance is unstable or poor.
- 2Record the exact code and check the operating instructions for the installed model.
- 3Arrange qualified service before continued operation.
Likely causes
What usually sits behind this code
The refrigeration cycle is operating abnormally.
The unit has detected a fault condition in the cooling circuit.
Contact support
Contact customer support if any of these apply
- !The code appears more than once.
- !Cooling performance is poor or stops altogether.
- !Refrigeration-system diagnosis is needed.
- - Panasonic's self-diagnosis article says to note the code and contact a qualified service technician for inspection, troubleshooting, and repairs.
- - This is a refrigerant-cycle fault label rather than a user-maintenance reminder.
Related codes
Nearby codes in this family
More ranges
More Panasonic air-conditioner ranges
Source notes
Source and scope
Source: Panasonic Cambodia HVAC
Panasonic's official self-diagnosis page lists F91 as 'Refrigerant cycle abnormality'.
Last reviewed: 2026-04-19
Panasonic says the self-diagnosis function is for identifying potential malfunctions. Repairs and complex troubleshooting should be handled by a qualified service technician.