What causes Daikin Mini Split U0?

A refrigerant leak, which Daikin lists first. A mini split's charge doesn't get used up, so low refrigerant almost always means a leak somewhere in the line set, flare connections or coils. A stop valve (service valve) at the outdoor unit that is closed or not fully open, often after a new installation. The refrigerant circuit was never charged correctly, for example a long line set without the extra charge the installation needs. A disconnected or faulty thermistor (temperature sensor): the discharge pipe, indoor or outdoor heat exchanger, room air or outdoor air sensor can all trigger a false U0. A defective electronic expansion valve, or a clogged refrigerant circuit, including ice formed by moisture in the refrigerant. Poor compression from a failing compressor, or on some commercial models a faulty low pressure sensor or outdoor main board.

How do I fix Daikin Mini Split U0?

Write down the code (and any sub code like U0-00) and roughly when it appeared, for example right after installation or after years of working fine. Turn the system off and switch off its breaker for a few minutes, then turn it back on. Daikin lists a power reset via the outdoor unit as one way to clear U0, but if the code comes back the cause is still there. Clean or replace the indoor unit's air filters and make sure nothing is blocking the indoor or outdoor unit. That doesn't fix a leak, but it rules out airflow problems that make the system struggle. Look along the outdoor line set for obvious damage, such as crushed or chewed insulation, but don't loosen or tighten any fittings yourself. If the system was installed recently, call the installer first. A closed stop valve or a missing charge for the line-set length is an installation problem and is usually covered. Don't buy a DIY recharge can. Daikin's procedure is to fix the leak and charge the correct amount shown on the nameplate, which takes recovery and weighing equipment and EPA certification.

When should I call a pro for Daikin Mini Split U0?

U0 returns after a power reset. A technician first checks the thermistors, since Daikin's troubleshooting starts with any disconnected or faulty sensor before the refrigerant circuit. The sensors are fine. The technician checks that the stop valves are fully open and checks the charge against the amount on the outdoor unit's nameplate. The charge is low. The leak must be found and repaired; if moisture or non-condensables are suspected, Daikin's corrective action is to recover, vacuum and recharge with virgin refrigerant. The charge is correct. The technician checks the expansion valve and the compressor, and on commercial systems the low pressure sensor and outdoor main board, as Daikin's flow directs. The system is still under warranty. Contact the installing contractor or a Daikin dealer before paying for refrigerant work.

Code: U0🔧 Daikin Mini Split

Daikin Error Code U0: Refrigerant Shortage (Insufficient Gas) (Meaning, Causes, Fixes)

Q: What does Daikin Mini Split U0 mean?

U0 on a Daikin system means the unit thinks it's short of refrigerant (Daikin's manuals call it "Insufficient Gas" or "Refrigerant shortage"). The most common cause is a refrigerant leak, but Daikin also lists a closed stop valve after installation, a disconnected or faulty temperature sensor, a bad expansion valve, a clogged refrigerant circuit and a weak compressor. A power reset can clear it for a while, but if U0 comes back you need a technician to find and fix the leak rather than just top it up. On Daikin ductless (FTX/FTXS-type) systems, U0 is "Insufficient Gas". The outdoor board compares how much power or current the compressor draws against how fast it's running, and on many models it also checks how much colder (or warmer) the indoor and outdoor coils are than the room and outdoor air. If those numbers look like a system that's low on refrigerant, it counts a gas shortage; Daikin's FTXS service manuals say the system shuts down after 4 detections in a row, and the counter resets if no error happens during the next 60 minutes of compressor running time. On Sky-Air and VRV commercial systems and on Daikin Altherma heat pumps, U0 (shown as U0-00 or with another sub code) is "Refrigerant shortage", and the unit stops operating. On some VRV outdoor units, U0 sub code 05 is only a warning and the system keeps running.

Reviewed 2026-10-24 · Based on 6 manufacturer & service sources

What the code means

On Daikin ductless (FTX/FTXS-type) systems, U0 is "Insufficient Gas". The outdoor board compares how much power or current the compressor draws against how fast it's running, and on many models it also checks how much colder (or warmer) the indoor and outdoor coils are than the room and outdoor air. If those numbers look like a system that's low on refrigerant, it counts a gas shortage; Daikin's FTXS service manuals say the system shuts down after 4 detections in a row, and the counter resets if no error happens during the next 60 minutes of compressor running time. On Sky-Air and VRV commercial systems and on Daikin Altherma heat pumps, U0 (shown as U0-00 or with another sub code) is "Refrigerant shortage", and the unit stops operating. On some VRV outdoor units, U0 sub code 05 is only a warning and the system keeps running.

Likely causes

A refrigerant leak, which Daikin lists first. A mini split's charge doesn't get used up, so low refrigerant almost always means a leak somewhere in the line set, flare connections or coils.
A stop valve (service valve) at the outdoor unit that is closed or not fully open, often after a new installation.
The refrigerant circuit was never charged correctly, for example a long line set without the extra charge the installation needs.
A disconnected or faulty thermistor (temperature sensor): the discharge pipe, indoor or outdoor heat exchanger, room air or outdoor air sensor can all trigger a false U0.
A defective electronic expansion valve, or a clogged refrigerant circuit, including ice formed by moisture in the refrigerant.
Poor compression from a failing compressor, or on some commercial models a faulty low pressure sensor or outdoor main board.

Safe DIY checks

⚠ Before you start

Turn off the breaker for both units before inspecting anything. Daikin's manuals warn to turn off the power switch before connecting or disconnecting connectors. Inverter outdoor units can hold a dangerous charge after power is off, and refrigerant lines can be hot or cold enough to burn. Refrigerant handling requires an EPA-certified technician, and newer Daikin units use R-32, which is mildly flammable, so leak repair and recharging should be left to a licensed HVAC pro.

Write down the code (and any sub code like U0-00) and roughly when it appeared, for example right after installation or after years of working fine.
Turn the system off and switch off its breaker for a few minutes, then turn it back on. Daikin lists a power reset via the outdoor unit as one way to clear U0, but if the code comes back the cause is still there.
Clean or replace the indoor unit's air filters and make sure nothing is blocking the indoor or outdoor unit. That doesn't fix a leak, but it rules out airflow problems that make the system struggle.
Look along the outdoor line set for obvious damage, such as crushed or chewed insulation, but don't loosen or tighten any fittings yourself.
If the system was installed recently, call the installer first. A closed stop valve or a missing charge for the line-set length is an installation problem and is usually covered.
Don't buy a DIY recharge can. Daikin's procedure is to fix the leak and charge the correct amount shown on the nameplate, which takes recovery and weighing equipment and EPA certification.

🛠 When to call a pro

U0 returns after a power reset. A technician first checks the thermistors, since Daikin's troubleshooting starts with any disconnected or faulty sensor before the refrigerant circuit.
The sensors are fine. The technician checks that the stop valves are fully open and checks the charge against the amount on the outdoor unit's nameplate.
The charge is low. The leak must be found and repaired; if moisture or non-condensables are suspected, Daikin's corrective action is to recover, vacuum and recharge with virgin refrigerant.
The charge is correct. The technician checks the expansion valve and the compressor, and on commercial systems the low pressure sensor and outdoor main board, as Daikin's flow directs.
The system is still under warranty. Contact the installing contractor or a Daikin dealer before paying for refrigerant work.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Refrigerant leak detector

For a technician to find the leak before recharging; a leak is the most common U0 cause.

Search eBay →

⚙

Daikin thermistor

Replace only if a technician finds a disconnected or out-of-range sensor; match the outdoor or indoor model number.

Search eBay →

⚙

Coil cleaner

Keeps the indoor and outdoor coils clean so airflow problems aren't confused with a refrigerant problem.

Search eBay →

Sources

Last reviewed 2026-10-24. Always confirm against the manual for your exact model number.

Daikin Error Code U0: Refrigerant Shortage (Insufficient Gas) (Meaning, Causes, Fixes)

What the code means

Likely causes

Safe DIY checks

🛠 When to call a pro

Parts that commonly fix it

Refrigerant leak detector

Daikin thermistor

Coil cleaner

Related codes

Sources