MrCool · Mini-Split Serious

F4 — Outdoor EEPROM / Memory Error

F4 indicates an outdoor unit EEPROM error — the outdoor control board cannot read its stored parameter data.

Keep using it?
Limited use only
DIY difficulty
Hard
Verified against
support.mrcool.com ↗

How to fix it

  1. Power-cycle at the breaker: off for five minutes, then back on. A one-time memory read error can clear on a clean restart.
  2. If F4 returns, call an HVAC technician. The stored-parameter memory lives on the outdoor control board, and the fix is board-level.
  3. What the technician will do: confirm the fault and replace the outdoor control board, then verify the replacement is configured for your model. If your area had a recent lightning storm or surge, mention it — and ask about outdoor surge protection while they are there.

Why it happens

Typical signs: Outdoor unit will not run · F4 on the display

  • Outdoor control board fault The EEPROM/memory on the outdoor PCB has failed or corrupted.

Parts you may need

If diagnosis points to a failed part, these are the common replacements. As an Amazon Associate we earn from qualifying purchases.

  • Mini-Split Outdoor Control Board Common replacement
    Amazon →

More MrCool mini-split codes

E1 E1 — Indoor/Outdoor Communication Error E2 E2 — Zero-Crossing Detection Error E3 E3 — Indoor Fan Speed Out of Control E4 E4 — Indoor Room Sensor (T1) Fault E5 E5 — Indoor Coil Sensor (T2) Fault F0 F0 — Overload / Current Protection

All MrCool codes → All mini-split codes →

Frequently asked questions

What does the F4 code mean on a MrCool mini-split?

F4 indicates an outdoor unit EEPROM error — the outdoor control board cannot read its stored parameter data.

What causes the F4 code on a MrCool mini-split?

Outdoor control board fault: The EEPROM/memory on the outdoor PCB has failed or corrupted.

Is it safe to keep using a MrCool mini-split with a F4 error?

Limited use only. This is rated a serious-severity fault.

How do I fix F4 on a MrCool mini-split?

Power-cycle at the breaker: off for five minutes, then back on. A one-time memory read error can clear on a clean restart. If F4 returns, call an HVAC technician. The stored-parameter memory lives on the outdoor control board, and the fix is board-level. What the technician will do: confirm the fault and replace the outdoor control board, then verify the replacement is configured for your model. If your area had a recent lightning storm or surge, mention it — and ask about outdoor surge protection while they are there.

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician. Verified against manufacturer documentation: support.mrcool.com.