F4 Serious Hard — consider a tech

MrCool Mini-Split F4 — Outdoor EEPROM / Memory Error

MrCool Mini-Split · Error code F4

What F4 Means

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

Symptoms

  • Outdoor unit will not run
  • F4 on the display

Common Causes

1
Outdoor control board fault

The EEPROM/memory on the outdoor PCB has failed or corrupted.

How to Fix It

  1. Power-cycle the unit at the breaker for a few minutes.
  2. If F4 returns, the outdoor control board typically needs replacement — a technician repair.

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.

Common replacement Mini-Split Outdoor Control Board View on 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 →

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician.