- HVAC
- Air conditioner
F91
Panasonic F91 on an air conditioner: refrigeration cycle abnormality
Risk level
High
Professional inspection is recommended.
Urgency
Medium
Quick answer
On Panasonic split units, F91 means a refrigeration cycle abnormality, linked to lack of refrigerant or a closed 3-way valve. Switch the unit off, turn off its circuit and call an F-gas certified technician.
Safety first
Stop and check this first
- Panasonic reserves repairs for professional technicians and electrical work for a licensed electrician. The board capacitor holds high voltage that must be discharged before work: do not open the unit.
- Panasonic warns that no substance other than the specified refrigerant, such as air, may enter the circuit, as it causes abnormally high pressure. Improvised top-ups are not acceptable.
Safe checks you can perform
- Reading the code with the remote
- Recent installation or repair
- 3-way valve and charge
Leave these tasks to a qualified professional
- Do not attempt this professional task: Find the leak before recharging
- Do not attempt this professional task: Test longer than 20 minutes
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Find the leak before recharging
What they doThe technician finds and repairs the loss before adding refrigerant, and does not recharge without checking the valve.
They must show youthe valve position and the leak point.
In writingamount charged, refrigerant and certificate number.
Test longer than 20 minutes
What they doAfter the repair the technician runs the unit for more than 20 minutes and reads the code again.
They must show youthe unit running that long with no code.
In writingdate and result.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Reading the code with the remote
- Who:
- you.
- How:
- if the unit stops and the TIMER lamp blinks, Panasonic says to read the code with the remote: hold CHECK for about 5 seconds and step through the codes; at the right one you hear four beeps and the operation lamp lights.
- Result that matters:
- that the confirmed code is F91.
- If you confirm F91:
- switch the unit off and give the code to an authorised dealer.
- If another code appears:
- this page does not apply; Panasonic notes some codes do not apply to every model.
- Evidence to keep:
- a photo of the remote with the confirmed code and the date.
Evidence: Panasonic air conditioner service manual PAPAGZ121215CE, CS-UE9PKE, CS-UE12PKE, CU-UE9PKE, CU-UE12PKE · Panasonic operating instructions, air conditioner CS-XZ and CU-XZ series
Recent installation or repair
- Who:
- you.
- How:
- check whether the unit was installed or its circuit worked on shortly before the fault.
- Result that matters:
- whether F91 has appeared since the first start-up.
- If it is recent:
- call the installer; Panasonic cites a closed 3-way valve.
- If it had run for a long time:
- lack of refrigerant gains weight.
- Evidence to keep:
- the installation job sheet or invoice with its date.
Evidence: Panasonic air conditioner service manual PAPAGZ121215CE, CS-UE9PKE, CS-UE12PKE, CU-UE9PKE, CU-UE12PKE · Panasonic operating instructions, air conditioner CS-XZ and CU-XZ series
3-way valve and charge
- Who:
- an F-gas certified technician.
- How:
- checks the 3-way valve position and the refrigerant charge, and searches for leaks.
- Result that matters:
- whether the valve is closed or refrigerant is missing.
- If the valve was closed:
- it is opened and confirmed as the cause.
- If refrigerant is missing:
- the leak is found and repaired before charging.
- Evidence to keep:
- a job sheet with valve position, measured charge and leak point.
Refrigerant circuit work: only an F-gas certified technician.
Evidence: Panasonic air conditioner service manual PAPAGZ121215CE, CS-UE9PKE, CS-UE12PKE, CU-UE9PKE, CU-UE12PKE
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- HVAC
- Brand
- Panasonic
- Product type
- Air conditioner
Known code variants
- F 91
- Panasonic F91
What it means
Panasonic defines F91 as a refrigeration cycle abnormality, judged when it occurs 2 times within 20 minutes, with the check being no refrigerant or a closed 3-way valve. Its low pressure prevention control detects it: if the compressor runs for 5 minutes continuously with total outdoor current between 0.83 and 1.05 A, and this happens twice within 20 minutes, the unit stops, the timer lamp blinks and F91 is shown. The code infers the problem from current, it does not measure the charge: the technician confirms it.
Warnings and stop conditions
- Highsource verified
Panasonic reserves repairs for professional technicians and electrical work for a licensed electrician. The board capacitor holds high voltage that must be discharged before work: do not open the unit.
Evidence: Panasonic air conditioner service manual PAPAGZ121215CE, CS-UE9PKE, CS-UE12PKE, CU-UE9PKE, CU-UE12PKE
- Mediumsource verified
Panasonic warns that no substance other than the specified refrigerant, such as air, may enter the circuit, as it causes abnormally high pressure. Improvised top-ups are not acceptable.
Evidence: Panasonic air conditioner service manual PAPAGZ121215CE, CS-UE9PKE, CS-UE12PKE, CU-UE9PKE, CU-UE12PKE
Symptoms and causes
Probable causes · in order
- Lack of refrigerantCommon
The cause Panasonic ties to gas leakage detection; confirmed by measuring the charge and searching for leaks.
Evidence: Panasonic air conditioner service manual PAPAGZ121215CE, CS-UE9PKE, CS-UE12PKE, CU-UE9PKE, CU-UE12PKE · Panasonic operating instructions, air conditioner CS-XZ and CU-XZ series
- 3-way valve closedPossible
The other check Panasonic cites; more likely if the code appears at the first start-up after installation.
Evidence: Panasonic air conditioner service manual PAPAGZ121215CE, CS-UE9PKE, CS-UE12PKE, CU-UE9PKE, CU-UE12PKE · Panasonic operating instructions, air conditioner CS-XZ and CU-XZ series
Virtual technician
Does F91 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
- 2
Panasonic operating instructions, air conditioner CS-XZ and CU-XZ series
Panasonic North America · 2025 · manual
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