HVAC Code Lookup

Daikin Mini-Split Code U2

Warning

Low-voltage detection or over-voltage detection. Either the indoor unit saw no zero-cross signal on its power supply for about 10 seconds, or the outdoor unit's DC bus dropped below roughly 150-200 V or spiked too high. The compressor stops and retries after a 3-minute standby.

Manual wording: “U2 Low-voltage detection or over-voltage detection”

Documented for: FTXS-L, FDXS-L, H-Series, FTXM-W/V, RMXS multi-split

Likely causes, most common first

  1. Supply voltage is not as specified
  2. Momentary fall of voltage
  3. Noise
  4. Disconnection of compressor harness
  5. Defective DC voltage detection circuit
  6. Defective over-voltage detection circuit
  7. Defective PAM control part

What you can safely check yourself

  • Check whether the house has had brownouts, flickering lights or a recent utility outage
  • Check the breaker or disconnect for the indoor and outdoor units is fully on
  • Turn the system off at the breaker or disconnect switch, wait a minute, and turn it back on once

When to call a technician

If the incoming power is steady and U2 persists, the outdoor unit's voltage detection circuit or board is at fault and needs a technician. Measuring supply voltage at the terminal board is not a homeowner job.

A Daikin mini-split throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.

Sources

Other Daikin codes