How House Works

Daikin U2: voltage drop or overvoltage

By How House Works EditorialBased on Daikin manualsChecked against sources Updated

Daikin remote controller display

U2

“DROP VOLTAGE OR MAIN CIRCUIT OVERVOLTAGE”

FTXM-WVJU9, FTXQ-ASBU9, FTX/FTXN-NMVJU, FTXS30/36 · FTXM-WVJU9 Operation Manual, p. 50; FTXQ-ASBU9 Operation Manual, p. 28; FTX/FTXN-NMVJU Operation Manual, p. 30; FTXS30/36 Operation Manual, p. 36
Technician

In the SYSTEM group. The FTXM-W/V service manual calls U2 “Low-voltage detection or over-voltage detection” (FTXM-W/V Service Manual SiUS042113EA, p. 96).

What it means

U2 comes from the unit’s own voltage detection circuits. In the FTXM-W/V service manual the outdoor unit sets it for low voltage when its DC voltage detection circuit reads below 162 V on the 09/12 class or 160 V on the 18/24 class, and for overvoltage when its over-voltage detection circuit signals the microcomputer. In both cases the compressor stops and restarts by itself after a 3-minute standby. On the indoor side the limit is a DC voltage below 140 V FTXM-W/V Service Manual SiUS042113EA, p. 106.

Other manuals set different limits. The FTX-W and FTXS-L manuals give 150–200 V for the outdoor unit and set U2 on the indoor side when there is no zero-cross detection of the power supply for about 10 seconds FTX-W Service Manual SiUS042228E, p. 76; FTXS-L Service Manual SiUS091133, p. 107. The FTK-B/FTX-B manual gives 180–196 V, depending on the model FTK-B/FTX-B Service Manual DAMA-SM-23-006, p. 64. All of these are readings of the unit’s internal detection circuits.

A stop without a code is a different case. With the OPERATION lamp lit, the unit may stop after a sudden large voltage fluctuation and start again by itself in about 3 minutes; after a power failure it also restarts in about 3 minutes FTXM-WVJU9 Operation Manual, pp. 46, 51; FTXS30/36 Operation Manual, pp. 34–35.

Check these first

  1. Check that the OPERATION lamp blinks at about 0.5-second intervals and read the code, as described in the Daikin code guide FTXM-WVJU9 Operation Manual, p. 49; FTXQ-ASBU9 Operation Manual, p. 27.
  2. Turn off the power with the circuit breaker, then restart with the remote controller FTXM-WVJU9 Operation Manual, p. 46; FTXQ-ASBU9 Operation Manual, p. 24; FTX/FTXN-NMVJU Operation Manual, p. 27. If you stopped the unit yourself, the manual’s caution is to wait at least 5 minutes after stopping before turning off the power, or water may leak FTXM-WVJU9 Operation Manual, p. 4. The manuals give the same step when the unit behaves strangely because of lightning or radio FTXM-WVJU9 Operation Manual, p. 48; FTXQ-ASBU9 Operation Manual, p. 26. After the breaker goes on, allow about 3 to 10 minutes before the unit runs FTXM-WVJU9 Operation Manual, p. 47.
  3. Watch the lamp. U2 is one of the “Other error codes” in the FTXM-WVJU9 and FTXQ-ASBU9 charts: if the lamp stays lit after the unit has run for a while, keep using it; if it blinks again, turn off the circuit breaker and call your dealer FTXM-WVJU9 Operation Manual, pp. 49–50; FTXQ-ASBU9 Operation Manual, pp. 27–28.
  4. If the circuit breaker cuts off the operation often, the manuals put that on the list of symptoms for which you turn off the breaker and call your dealer at once FTXM-WVJU9 Operation Manual, p. 51; FTXQ-ASBU9 Operation Manual, p. 29.
  5. If lightning could strike nearby, the manual says to stop the unit and turn off the circuit breaker to protect the system FTXM-WVJU9 Operation Manual, p. 51.

FTXS30/36 owners have the general steps for a flashing lamp, ending with a call to the service shop FTXS30/36 Operation Manual, p. 34.

When to call a licensed technician

The FTXM-W/V service manual lists these causes for U2 FTXM-W/V Service Manual SiUS042113EA, p. 106:

  • power supply voltage out of specification, noise, a momentary drop of voltage, or a momentary power failure;
  • a defective DC voltage detection circuit, over-voltage detection circuit or PAM control part;
  • a disconnected compressor harness, or a short circuit inside the fan motor winding;
  • a defective outdoor unit PCB or indoor unit PCB.

The AXVJU manual gives nearly the same list AXVJU Service Manual SM-5WM-Y-NA-B1, p. 58. Checking the supply voltage and the unit’s circuits is electrical work: the owner’s manual says not to do electrical or grounding work unless you are licensed to do so FTXM-WVJU9 Operation Manual, p. 4, and the service manual warns that working on equipment connected to power may cause an electric shock and that the outdoor unit’s step-up capacitor must be discharged before repair work FTXM-W/V Service Manual SiUS042113EA, pp. 2–3.

Notes for different models

  • FTX/FTK-BXVJU, the remote manuals and the AXVJU service manual call U2 “DC voltage out of range” FTX/FTK-BXVJU Operation Manual, p. 1, section 9; BRC52B Remote Controller Manual, p. 1-4; BRC51D61 Wired Remote Controller Manual, p. 12; AXVJU Service Manual SM-5WM-Y-NA-B1, p. 34. The FTX-W and FTXS-L service tables call it “Low-voltage detection or over-voltage detection” FTX-W Service Manual SiUS042228E, p. 68; FTXS-L Service Manual SiUS091133, p. 94.
  • The FTX/FTK-BXVJU and remote lists also have P1, “Open phase or voltage unbalance”, a separate code FTX/FTK-BXVJU Operation Manual, p. 1, section 9.

Related Daikin codes

  • U4 “FAILURE OF TRANSMISSION (BETWEEN INDOOR UNIT AND OUTDOOR UNIT)”
  • UA “INDOOR-OUTDOOR UNIT COMBINATION FAULT”
  • E8 “OVERCURRENT INPUT”

See also

Other ductless mini-splits: Fujitsu, Mitsubishi Electric, MrCool

All Daikin codes

Daikin is a trademark of its owner. How House Works is not affiliated with or endorsed by Daikin.

Sources

  1. Daikin Comfort Technologies North America (document library). FTXM-WVJU9 Operation Manual. 3P686871-1A, page stamp 2022/05/30; covers FTXM09/12/18/24WVJU9. Listed under ATMOSPHERA in Daikin's document library.. Accessed Oct 13, 2026.
  2. Daikin Comfort Technologies North America (document library). FTXQ-ASBU9 Operation Manual. 3P741457-13J, English; page stamp 2024/11/19; covers FTXQ09ASBU9 and FTXQ12ASBU9. Listed under OTERRA 115V. The library list shows only the French and Spanish files of this manual; the English file is served at this address.. Accessed Oct 13, 2026.
  3. Daikin Comfort Technologies North America (document library). FTX/FTXN-NMVJU Operation Manual. 3P379751-4C, page stamp 11/6/2015; covers FTX09/12/15/18/24NMVJU and FTXN09/12/18/24NMVJU. Not in Daikin's current library list; the file is still served from daikincomfort.com.. Accessed Oct 13, 2026.
  4. Daikin Comfort Technologies North America (document library). FTXS30/36 Operation Manual. 3P228444-4K, page stamp 3/28/2013; covers FTXS30HVJU, FTXS36HVJU, FTXS30LVJU and FTXS36LVJU. Not in Daikin's current library list; the file is still served from daikincomfort.com.. Accessed Oct 13, 2026.
  5. Daikin Comfort Technologies North America (document library). FTX/FTK-BXVJU Operation Manual. 3P601789-2 E (cover label); no printed date; covers FTX, FTXB and FTK09/12/18/24BXVJU; R410A. A poster with one page per language (English, Spanish, French) and no page numbers: citations give PDF page 1 and the poster section. The same file is also listed under ENTRA.. Accessed Oct 13, 2026.
  6. Daikin Comfort Technologies North America (document library). BRC52B Remote Controller Manual. OM-BRC52B-0617(2)-DAIKIN USA, Part No. R08019046595B; print stamp 10/30/2017; covers remote controllers BRC52B61/62/63/64/65. Does not name the indoor units. The library lists it under ENTRA.. Accessed Oct 13, 2026.
  7. Daikin Comfort Technologies North America (document library). BRC51D61 Wired Remote Controller Manual. R08019049297B; print stamp 7/12/2022. Does not name the indoor units. The library lists it under OTERRA (cooling only) and ENTRA.. Accessed Oct 13, 2026.
  8. Daikin Comfort Technologies North America (document library). FTXM-W/V Service Manual SiUS042113EA. SiUS042113EA, revision of 01/2023; covers FTXM09/12/18/24WVJU9 and FTXM-VVJU with RXM outdoor units. Accessed Oct 13, 2026.
  9. Daikin Comfort Technologies North America (document library). FTK-B/FTX-B Service Manual DAMA-SM-23-006. DAMA-SM-23-006, first edition 04/2023; covers FTK09/12/18/24BXVJU and FTX09/12/18/24BXVJU with RK/RX-BXVJU outdoor units. Accessed Oct 13, 2026.
  10. Daikin Comfort Technologies North America (document library). AXVJU Service Manual SM-5WM-Y-NA-B1. SM-5WM-Y-NA-B1; no printed date (PDF created 2021-09-29); covers FTKB/FTKN/FTXB/FTXN09/12/18/24AXVJU. Listed under ENTRA.. Accessed Oct 13, 2026.
  11. Daikin Comfort Technologies North America (document library). FTX-W Service Manual SiUS042228E. SiUS042228E, first edition 10/2022; covers FTX30/36WVJU9 with RK30/36WMVJU9 or RX30/36WMVJU9. Listed under POLARA.. Accessed Oct 13, 2026.
  12. Daikin Comfort Technologies North America (document library). FTXS-L Service Manual SiUS091133. SiUS091133; no printed date (PDF created 2013-01-11); covers FTXS09–36LVJU and FDXS09/12LVJU. Not in Daikin's current library list; the file is still served from daikincomfort.com.. Accessed Oct 13, 2026.