HVAC Code Lookup

Daikin Mini-Split Code U0

Warning

Refrigerant shortage. The control compared input current, compressor speed, discharge pipe temperature and expansion valve position and concluded the system is low on refrigerant. On RMXS multi-split systems it reads as low pressure drop due to refrigerant shortage or an expansion valve fault.

Manual wording: “U0 Refrigerant shortage”

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

Likely causes, most common first

  1. Refrigerant shortage (refrigerant leakage)
  2. Closed stop valve
  3. Disconnection of the discharge pipe, indoor or outdoor heat exchanger, room or outdoor temperature thermistor
  4. Poor compression performance of compressor
  5. Defective electronic expansion valve
  6. Refrigerant system clogging / incorrect piping (multi-split)

What you can safely check yourself

  • Check and replace the indoor unit air filters
  • Check the outdoor unit is clear of snow, leaves and debris
  • Note whether cooling or heating has been getting gradually weaker over weeks - that pattern points to a leak

When to call a technician

U0 means a technician needs to leak-check and weigh in charge. Topping off refrigerant without finding the leak is illegal to do yourself and just repeats the problem.

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