How House Works

Daikin A5: freeze-up or high pressure protection

By How House Works EditorialBased on Daikin manualsChecked against sources Updated

Daikin remote controller display

A5

“HIGH PRESSURE CONTROL OR FREEZE-UP PROTECTOR”

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 INDOOR UNIT group. The FTXM-W/V service manual calls A5 “Freeze-up protection control/heating peak-cut control”: freeze-up protection stops operation when the indoor heat exchanger is below 32°F (0°C) in cooling, and peak-cut control acts when it is above 140–144°F (60–62°C) in heating (FTXM-W/V Service Manual SiUS042113EA, pp. 96, 98).

What it means

A5 is a protection code read from the indoor heat exchanger thermistor. In the FTXM-W/V service manual it covers two controls. In cooling, freeze-up protection stops operation when the indoor heat exchanger is below 32°F (0°C). In heating, the peak-cut control (operation halt, outdoor fan stop and similar) acts when the indoor heat exchanger is above 140–144°F (60–62°C) FTXM-W/V Service Manual SiUS042113EA, p. 98. The FTXS-L manual gives 140–149°F (60–65°C) for heating, depending on the model FTXS-L Service Manual SiUS091133, p. 97. The FTK-B/FTX-B manual gives above 141.8°F (61°C) and applies the high pressure control to heat pump models only FTK-B/FTX-B Service Manual DAMA-SM-23-006, p. 60.

The owner’s tables put A5 in the INDOOR UNIT group FTXM-WVJU9 Operation Manual, p. 50. Its name changes with the manual: see the notes below.

Check these first

The owner’s manuals have no step written for A5 itself. Their general checks for a blinking lamp include the air filters, and the service manual lists a clogged air filter of the indoor unit among the causes of A5 FTXM-W/V Service Manual SiUS042113EA, p. 98:

  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.
  2. Clean the air filters if they are dirty FTXM-WVJU9 Operation Manual, p. 46; FTXQ-ASBU9 Operation Manual, p. 24, as the owner’s manual describes and with its cautions FTXM-WVJU9 Operation Manual, pp. 41–42; FTXQ-ASBU9 Operation Manual, pp. 19–20. Before cleaning, stop the operation and turn off the circuit breaker, and do not touch the aluminum fins of the indoor unit. The FTXM-WVJU9 manual adds two cautions for the front panel: “When removing or attaching the front panel, stand on a solid, stable base and take care not to fall.” and “When removing or attaching the front panel, support the panel securely with your hand to prevent it from falling.” FTXM-WVJU9 Operation Manual, p. 42.
  3. Check for anything blocking the air inlet or air outlet of the indoor or outdoor unit. Stop the unit, turn off the circuit breaker, remove the obstruction, 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. 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.
  4. Watch the lamp. If it still blinks, the manuals say to check the error code and consult your dealer FTXM-WVJU9 Operation Manual, p. 46. In the FTXM-WVJU9 and FTXQ-ASBU9 charts A5 is one of the “Other error codes”: if the lamp blinks again after running, turn off the circuit breaker and call your dealer FTXM-WVJU9 Operation Manual, pp. 49–50; FTXQ-ASBU9 Operation Manual, pp. 27–28.

The FTXS30/36 manual gives the same filter and obstacle checks for a flashing lamp, then a call to the service shop FTXS30/36 Operation Manual, p. 34.

When to call a licensed technician

The other causes in the FTXM-W/V service manual are short-circuited air, dust accumulation on the indoor heat exchanger, a defective indoor heat exchanger thermistor and a defective indoor unit PCB FTXM-W/V Service Manual SiUS042113EA, p. 98. The AXVJU manual adds a dirty fan blower AXVJU Service Manual SM-5WM-Y-NA-B1, p. 36.

The FTXM-WVJU9 manual gives owners no way to clean the coil or the fan. It says to consult the installation contractor for cleaning and that incorrect cleaning of the inside can break plastic parts and cause water leakage or electric shock; where a dirty heat exchanger or fan gives off an odor, it recommends having the indoor unit cleaned and consulting your dealer FTXM-WVJU9 Operation Manual, pp. 4, 48. It also recommends periodic maintenance by a qualified contractor in addition to regular cleaning by the user FTXM-WVJU9 Operation Manual, p. 44. The thermistor and the PCB are technician work.

Notes for different models

  • FTX/FTK-BXVJU: “Antifreeze” FTX/FTK-BXVJU Operation Manual, p. 1, section 9. The remote manuals: “ANTIFREEZE (COOLING)/HEAT EXCHANGER OVERHEAT (HEATING)” BRC52B Remote Controller Manual, p. 1-3; BRC51D61 Wired Remote Controller Manual, p. 11. The AXVJU service manual: “ANTIFREEZE PROTECTION OR HIGH PRESSURE CONTROL” AXVJU Service Manual SM-5WM-Y-NA-B1, p. 34.
  • The FTX/FTK-BXVJU list also has UH, “Antifreeze (other rooms)”, a different code FTX/FTK-BXVJU Operation Manual, p. 1, section 9.
  • F6, “HIGH PRESSURE CONTROL (IN COOLING)”, is a separate code, set from the outdoor heat exchanger thermistor in cooling FTXM-WVJU9 Operation Manual, p. 50; FTXM-W/V Service Manual SiUS042113EA, p. 124.

Related Daikin codes

  • C4 “FAULTY HEAT EXCHANGER TEMPERATURE SENSOR”
  • F6 “HIGH PRESSURE CONTROL (IN COOLING)”
  • UH “Antifreeze (other rooms)”

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). 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.