Midea Mini Split Error Code F1: Outdoor Ambient Temperature Sensor (T4) Fault (Meaning, Causes, Fixes)
What the code means
Midea's Oasis Plus 3D Inverter service manual lists F1 as "Outdoor ambient temperature sensor T4 open circuit or short circuit", and the same meaning appears in Midea's Mission2 3D Inverter manual and in the error tables for Midea cassette, duct, console and floor-standing units. T4 is a thermistor (a resistor that changes with temperature) on the outdoor unit that measures the outside air temperature, and the control board uses it to manage things like heating, defrost and compressor speed. Midea's troubleshooting section groups F1 with E4 (indoor room sensor T1), E5 (indoor coil sensor T2), F2 (condenser coil sensor T3) and F3 (compressor discharge sensor): the code shows when the sensor's sampling voltage is lower than 0.06 V or higher than 4.94 V, which only happens when the circuit is open, shorted, or disconnected. On Midea cassette and duct units with indicator lamps instead of a display, the manual shows F1 as the timer lamp on with the operation lamp flashing twice.
Likely causes
- A loose, unplugged or corroded T4 sensor connector at the outdoor control board. Midea's first check is the connection between the sensor and the board.
- A wiring mistake or damaged sensor lead, for example after outdoor service or animal damage to the wiring.
- A failed T4 sensor that reads open or shorted. Midea's fix is to replace the sensor if its resistance is outside the chart in the service manual.
- A faulty outdoor control board, which Midea lists last, after the wiring and sensor check out.
Safe DIY checks
Turn off the breaker for the outdoor unit before any inspection, and leave the covers on. Inverter mini splits store a dangerous charge in their capacitors even after the power is off, and Midea's manual says to make sure they are fully discharged before troubleshooting. Midea's newer models also use R32 refrigerant, which is mildly flammable, so leave sensor, board and refrigerant work to a licensed HVAC technician.
- Write down the exact code. F1 is the outdoor air sensor, while F2 is the outdoor coil sensor, F3 is the discharge sensor and E4 or E5 are indoor sensors, so the code tells a technician which part to test.
- Turn the system off and switch off its breaker for a few minutes, then restore power and try again. A one-time glitch can clear, but if F1 returns the sensor circuit needs checking.
- Look at the outdoor unit from the outside. Note any chewed, pinched or damaged wiring, storm damage, or signs that the unit was recently serviced or moved, and tell your technician.
- Don't open the outdoor unit's covers yourself. Midea's service manual warns that electricity remains in the capacitors even when the power supply is off.
- If the system is still under warranty or was recently installed, contact the installing contractor before paying for parts.
🛠 When to call a pro
- F1 comes back after a power reset. A technician checks the T4 connector and wiring at the outdoor control board first, which is Midea's first step.
- The wiring is good. The technician unplugs T4 and measures its resistance against Midea's sensor chart; for example, the T1 to T4 sensors read 10 kilohms at 25 °C (77 °F) and about 35.2 kilohms at 0 °C (32 °F). If the reading is out of range, the sensor is replaced.
- The sensor reads correctly and is properly connected. Midea's remedy is to replace the outdoor control board.
- You also see F2 or F3 at other times. Midea's disassembly steps show the T3, T4 and discharge sensor connectors plugging into the outdoor board side by side, so a technician should check that whole connector area, not just T4.
Parts that commonly fix it
Always match the part number to your exact model.
Outdoor ambient temperature sensor (T4)
Replace only if it measures out of range on Midea's resistance chart; match the outdoor unit model number before ordering.
Search eBay →Sources
- Midea Oasis Plus 3D Inverter Series service manual (2018, R32): error code table (F1 = outdoor ambient temperature sensor T4 open or short circuit), section 5.6 E4/E5/F1/F2/F3 diagnosis, capacitor safety caution, and T1-T4 sensor resistance table
- Midea Mission2 3D Inverter Series service manual, p.95 (E4/E5/F1/F2/F3 open or short circuit of temperature sensor: 0.06 V / 4.94 V detection, wiring, sensor, PCB), via ManualsLib
- Midea cassette and duct (MCA3/MCD) service manual, electrical control troubleshooting tables (F1 = T4 temperature sensor open or short circuit; timer lamp on, operation lamp 2 flashes), via Clim-Cash
Last reviewed 2026-10-24. Always confirm against the manual for your exact model number.