What causes Haier Mini Split bA?

The unit doesn't need a leak sensor, but the leak sensor DIP switch was left in its factory ON position (DIP switch 3-2 on highwall indoor units). The room does need a leak sensor, but the sensor (Haier accessory UALS01A on highwall units) was never installed. The leak sensor is installed but not plugged in, or its plug came loose (connector CN3 on the highwall indoor board), and the unit was then powered up. Less likely: a damaged leak sensor wire or a faulty sensor or indoor board, if the sensor and switch setting both check out.

How do I fix Haier Mini Split bA?

If this is a new installation, call the installing contractor first. Haier ties bA to a setup step during installation, so it's usually a quick fix for them. Turn the system off at the breaker or disconnect for a minute and back on once. If the sensor plug only came loose, this won't fix it, but it rules out a one-time glitch. Don't open the indoor unit, change DIP switches or plug in sensor wires yourself. Whether your room needs a leak sensor depends on the room size and refrigerant charge, which the installer has to work out under the safety code. Tell the technician the code (bA), that the fan runs on high with the compressor off, and the model numbers of the indoor and outdoor units.

When should I call a pro for Haier Mini Split bA?

Work out whether this indoor unit needs a refrigerant leak sensor, using the room size and total refrigerant charge tables in the indoor and outdoor installation instructions (Haier bases them on UL 60335-2-40 Edition 4, with an altitude adjustment factor). If no sensor is needed, power down and set the leak sensor DIP switch OFF (DIP switch 3-2 on highwall indoor units), then power the system back up. Haier says bA clears once the switch is OFF and the system is power cycled. Other indoor unit types use a different switch: Haier's compact cassette instructions say to flip DIP switch 1-5 to ON when no sensor is needed, so check the instructions for the exact model. If a sensor is needed, install it (UALS01A on highwall units, mounted on the bracket on the back of the unit) and plug it into CN3 on the indoor PCB (CN23 on compact cassettes), then power cycle the system. Verify the sensor as Haier describes: unplug it with the system running and within about 30 seconds the unit should show Ac, run the fan on high and stop the compressor; power up with it unplugged and it should show bA. Reconnect it and confirm normal operation. If bA stays with the sensor connected and the switch set correctly, check the sensor wire and then the sensor and indoor board.

Code: bA🔧 Haier Mini Split

Haier Mini Split Error Code bA: Leak Sensor Switch On but No Sensor Found (Meaning, Causes, Fixes)

Q: What does Haier Mini Split bA mean?

bA on a newer Haier R-454B mini split means the indoor unit is set to expect a refrigerant leak sensor but can't find one when it powers up. It's almost always an installation setting: either the leak sensor was never installed or plugged in, or the installer forgot to turn off the leak sensor DIP switch on a unit that doesn't need one. The indoor fan runs on high and the compressor stays off until it's fixed, so call your installer. Haier's R-454B leak sensor code list defines bA as "Sensor DIP switch enabled but no sensor detected" ("No Leak Sensor Detected While Leak Sensor Dip Switch is ON"). Haier indoor units on R-454B refrigerant ship with the leak sensor DIP switch ON, meaning they look for a refrigerant leak sensor. Not every room needs one: the installer decides from the room size and the refrigerant charge. If no sensor is needed, the installer must flip the switch OFF (DIP switch 3-2 on highwall units), and Haier's highwall installation instructions say that missing this step will result in error code bA. Haier also says that if the system is powered up with the leak sensor disconnected, the indoor unit shows bA, runs the indoor fan at high speed and turns the outdoor compressor off. bA is not a refrigerant leak by itself; an active leak shows as AA, and losing the sensor while the unit is already running shows as Ac.

Reviewed 2026-10-24 · Based on 3 manufacturer & service sources

What the code means

Haier's R-454B leak sensor code list defines bA as "Sensor DIP switch enabled but no sensor detected" ("No Leak Sensor Detected While Leak Sensor Dip Switch is ON"). Haier indoor units on R-454B refrigerant ship with the leak sensor DIP switch ON, meaning they look for a refrigerant leak sensor. Not every room needs one: the installer decides from the room size and the refrigerant charge. If no sensor is needed, the installer must flip the switch OFF (DIP switch 3-2 on highwall units), and Haier's highwall installation instructions say that missing this step will result in error code bA. Haier also says that if the system is powered up with the leak sensor disconnected, the indoor unit shows bA, runs the indoor fan at high speed and turns the outdoor compressor off. bA is not a refrigerant leak by itself; an active leak shows as AA, and losing the sensor while the unit is already running shows as Ac.

Likely causes

The unit doesn't need a leak sensor, but the leak sensor DIP switch was left in its factory ON position (DIP switch 3-2 on highwall indoor units).
The room does need a leak sensor, but the sensor (Haier accessory UALS01A on highwall units) was never installed.
The leak sensor is installed but not plugged in, or its plug came loose (connector CN3 on the highwall indoor board), and the unit was then powered up.
Less likely: a damaged leak sensor wire or a faulty sensor or indoor board, if the sensor and switch setting both check out.

Safe DIY checks

⚠ Before you start

R-454B is a mildly flammable (A2L) refrigerant, and the leak sensor is a safety device. Only a licensed HVAC technician should decide whether a sensor is required, change DIP switch settings, or open the indoor unit. Never disable the sensor switch on a unit that needs a sensor just to clear the code.

If this is a new installation, call the installing contractor first. Haier ties bA to a setup step during installation, so it's usually a quick fix for them.
Turn the system off at the breaker or disconnect for a minute and back on once. If the sensor plug only came loose, this won't fix it, but it rules out a one-time glitch.
Don't open the indoor unit, change DIP switches or plug in sensor wires yourself. Whether your room needs a leak sensor depends on the room size and refrigerant charge, which the installer has to work out under the safety code.
Tell the technician the code (bA), that the fan runs on high with the compressor off, and the model numbers of the indoor and outdoor units.

🛠 When to call a pro

Work out whether this indoor unit needs a refrigerant leak sensor, using the room size and total refrigerant charge tables in the indoor and outdoor installation instructions (Haier bases them on UL 60335-2-40 Edition 4, with an altitude adjustment factor).
If no sensor is needed, power down and set the leak sensor DIP switch OFF (DIP switch 3-2 on highwall indoor units), then power the system back up. Haier says bA clears once the switch is OFF and the system is power cycled.
Other indoor unit types use a different switch: Haier's compact cassette instructions say to flip DIP switch 1-5 to ON when no sensor is needed, so check the instructions for the exact model.
If a sensor is needed, install it (UALS01A on highwall units, mounted on the bracket on the back of the unit) and plug it into CN3 on the indoor PCB (CN23 on compact cassettes), then power cycle the system.
Verify the sensor as Haier describes: unplug it with the system running and within about 30 seconds the unit should show Ac, run the fan on high and stop the compressor; power up with it unplugged and it should show bA. Reconnect it and confirm normal operation.
If bA stays with the sensor connected and the switch set correctly, check the sensor wire and then the sensor and indoor board.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Haier refrigerant leak sensor (UALS01A)

Only if the room size and charge call for a sensor and none is installed. Confirm the part for your exact indoor model.

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⚙

Digital multimeter

For a technician checking the sensor wire if bA won't clear.