F1 Moderate Moderate DIY

MrCool Mini-Split F1 — Outdoor Ambient Sensor (T4) Fault

MrCool Mini-Split · Error code F1

What F1 Means

F1 means the outdoor ambient-temperature sensor (T4 thermistor) is open or shorted.

Symptoms

  • Outdoor unit behaves oddly or stops
  • F1 on the display

Common Causes

1
Failed T4 sensor

The outdoor ambient thermistor has failed.

2
Loose connector at the outdoor board

The sensor plug is loose or corroded.

How to Fix It

  1. Power off at the breaker and open the outdoor unit cover.
  2. Locate the T4 ambient sensor and reseat its connector.
  3. Test/replace the thermistor if out of range.

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 Sensor Kit 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.