Fujitsu air conditioner 51 error code: indoor fan motor fault

What the 51 code means

Error 51 on a Fujitsu mini-split means the indoor fan motor is running too slowly. Fujitsu says it triggers when the fan's actual speed stays below a third of its target for more than 56 seconds. The lamps show 5 operation blinks and 1 timer blink.

The indoor fan is a DC motor that reports its speed back to the board. If the board asks for a speed and the fan cannot reach a third of it for nearly a minute, the board assumes the fan is jammed or failing and shuts the unit down.

Fujitsu's diagnosis checks three things: that the fan turns, the temperature around the motor, and the motor's resistance values.

Common causes

Listed from most to least common.

1. Blower wheel blocked or caught on something
2. Blower wheel clogged with dust or mold
3. Very hot surroundings around the motor
4. Indoor fan motor failed
5. Indoor controller board fault

How to fix the 51 code

Unplug the air conditioner or switch it off at the breaker before removing any panel or filter.

1. 1

   Step 1: Turn the power off

   Switch off the breaker before looking at the indoor unit.

2. 2

   Step 2: Check the blower turns

   Open the front panel, remove the filters and look at the long blower wheel behind the vanes. Fujitsu's first check is whether the fan turns freely by hand with the power off. Use a wooden spoon handle, not your fingers.

3. 3

   Step 3: Look for blockages

   Remove anything you can reach that is stopping the fan, such as a loose filter or debris. Heavy dust or black mold on the blower wheel needs a professional cleaning.

4. 4

   Step 4: Reset and test

   Refit the filters and panel, restore power and run Fan mode on high. Listen for scraping or a fan that starts and stops.

You'll need: Flashlight.

How to reset the Fujitsu air conditioner

1. Turn the system off with the remote or wired controller.
2. Switch off the breaker for the system, and the outdoor disconnect switch if there is one. Leave the power off for at least 5 minutes.
3. Restore power and turn the unit back on. The compressor normally waits a few minutes before starting, so give it time before judging.
4. If the same code or blink pattern comes back, the fault is still there. Work through the fix steps above, or call a Fujitsu contractor or other licensed HVAC technician.

When to call a technician

If the fan turns freely and 51 returns, a technician needs to test the fan motor's resistance and the controller board. Replacing the motor means taking the indoor unit apart.

A typical repair for this code costs $200–$650 in the US, including parts and labor. Prices vary by area and model.

Models this applies to

• Halcyon wall-mounted mini-splits (ASU indoor, AOU outdoor)
• Halcyon floor, ceiling cassette and slim duct units (AGU, AUU, ARU)
• Halcyon multi-zone systems (RLF series)
• Ducted and ceiling-suspended units (RGLX, RULX series)

Codes can differ slightly between models. Your owner's manual is the final word and is available from Fujitsu support.

Frequently asked questions