MrCool Mini Split Error Codes: Complete Master List (2026)

When a MrCool unit throws an error code, the unit is telling you exactly what's wrong. The trick is decoding what the code means. Below is every error code across the MrCool product lines — DIY, EasyPro, Advantage, Universal — with the cause, the test, and the fix.

If you're new to mini split troubleshooting, start with our mini split not cooling guide for diagnostic basics. For specific failures, find your code below.

How MrCool Codes Work

The codes break into four families:

• E codes = sensor or sensor-circuit faults (E1-E8 typical)
• F codes = fan, pressure, or compressor protection trips (F1-F5 typical)
• P codes = inverter and power protection (P0, P1, P4, P6, PA, PF)
• L, H, U, C codes = miscellaneous (less common, model-specific)

Codes display on the indoor unit's LED screen or via a series of LED blinks on units without displays. Some codes will clear on a power cycle; others won't until the underlying problem is fixed.

E Codes (Sensor Faults)

E1 — Indoor Air Temperature Sensor Fault

Cause: The indoor unit's room temperature sensor is open or shorted. Most often caused by a loose connector at the sensor or board. Fix: Power down. Open the indoor unit. Locate the indoor air temp sensor (small sensor on a wire near the air intake). Reseat the connector. If E1 persists after reset, the sensor needs replacement (~$25 part, 30-minute job).

E2 — Indoor Coil Sensor Fault

Cause: The evaporator coil temperature sensor is faulty. Fix: Same procedure as E1, but the sensor is mounted into the coil itself. Confirm the resistance reading at the sensor (typically 10-15kΩ at room temp).

E3 — Outdoor Sensor or Compressor Issue

Cause: Either an outdoor temperature sensor fault or a compressor protection trip caused by a related sensor. Fix: Inspect outdoor sensor. If sensor reads correctly but E3 persists, check for compressor protection conditions (high pressure, low pressure, overheating).

E4 — Outdoor Coil Sensor Failure

Cause: The condenser coil temperature sensor is reading out of range. Fix: Same test/replace procedure as E1/E2 but the sensor is at the outdoor unit, mounted into the coil.

E5 — Communication Error Between Indoor and Outdoor

Cause: Control wire fault between units. Causes: loose terminal, damaged wire, rodent damage, incorrect wire gauge. Fix: Power down both units. Inspect the 4-conductor control wire from end to end. Check for damaged insulation, loose terminals, or polarity reversal at either terminal block.

E6 — Indoor Fan Motor Fault

Cause: The indoor blower motor isn't reaching commanded speed. Fix: Disassemble indoor unit. Check that the blower wheel spins freely (sometimes mold buildup blocks it). Test motor capacitor if present. If motor is bound or buzzing without spinning, replacement is needed (~$75-$200 part).

E7 — EEPROM / Memory Error

Cause: Control board memory is corrupted, often from a power surge. Fix: Power down for 5 minutes, then restart. If E7 returns, the control board needs replacement (~$200-$500 part). Surge protection at the disconnect prevents recurrence.

E8 — Power Supply or Wiring Fault

Cause: Voltage out of range, miswired control circuits, or excessive current draw on the control circuit. Fix: Verify voltage at both terminal blocks (should be within 10% of nameplate spec). Check for shorts on control wiring.

F Codes (Fan, Pressure, Compressor Protection)

F1 — Outdoor Fan Motor Fault

Cause: Outdoor condenser fan isn't running or running below commanded speed. Fix: Capacitor test first ($15-$30 part if it fails). If cap is good and fan still won't spin, motor replacement.

F2 — Outdoor Fan Failure (Rotor Lock)

Cause: Outdoor fan motor is mechanically locked. Common in winter when ice forms on the fan blade. Fix: Power down. Manually rotate the fan blade (it should spin freely). Clear any ice or debris.

F3 — High Pressure Switch Trip

Cause: Refrigerant high-side pressure exceeded the safety limit. Causes ranked: dirty outdoor coil (most common), blocked outdoor airflow, refrigerant overcharge, defrost cycle malfunction. Fix: Clean the outdoor coil thoroughly. Verify nothing is restricting airflow within 18 inches of the unit. If F3 persists after cleaning, refrigerant charge needs verification by a licensed tech.

F4 — Low Pressure Switch Trip

Cause: Refrigerant low-side pressure dropped below safety limit. Almost always indicates a refrigerant leak. Fix: Look for oily residue at flare fittings, line set joints, and Schrader valves. F4 with no other obvious cause = call a licensed tech to find and fix the leak. EPA Section 608 makes this a non-DIY repair.

F5 — Compressor Overcurrent Protection

Cause: Compressor drew more current than the safety limit. Causes: stuck compressor, locked rotor, high pressure trip. Fix: Power down for 30 minutes (resets compressor protection). Restart. If F5 returns immediately, compressor diagnosis needed by a tech.

P Codes (Inverter and Power Protection)

P0 — Module Protection

Cause: The inverter's IGBT module hit a self-protection threshold (overheat, overcurrent, or undervoltage). Fix: Power cycle for 5 minutes. If P0 returns within minutes of restart, module replacement may be needed.

P1 — Voltage Out of Range

Cause: Supply voltage below 187V or above 264V on a 230V circuit (proportionally for 115V). Fix: Measure voltage at the disconnect with a multimeter. If voltage is normal at the disconnect but P1 persists, check for voltage drop along the supply circuit (undersized wire, loose connections).

P4 — Compressor Phase Sequence (3-phase units only)

Cause: Phase reversal on Universal three-phase commercial models. Fix: Swap any two of the three line conductors at the disconnect to correct phase rotation.

P6 — Compressor Discharge Temperature

Cause: Refrigerant discharge gas temperature exceeded 230°F. Causes: refrigerant undercharge, restricted metering device, dirty outdoor coil. Fix: Clean outdoor coil first. If P6 persists, refrigerant charge and metering device need professional verification.

PA — AC Current Protection

Cause: Inverter input current exceeded threshold. Often caused by undersized wiring or breaker. Fix: Verify breaker and wire sizing match the unit's MCA (minimum circuit ampacity) and MOCP (max overcurrent protection) specs from the nameplate.

PF — Power Filter Fault

Cause: Input line filter (suppresses electrical noise) is damaged. Fix: Filter replacement, ~$50 part. Surge protection prevents recurrence.

H Codes (Misc High-Priority)

H6 — Indoor Fan Motor Failure (Rotor Lock)

Cause: Indoor blower motor mechanically locked. Often from heavy mold buildup on the blower wheel. Fix: Disassemble indoor unit. Clean blower wheel thoroughly (scrubbing required). If wheel spins freely after cleaning, restart. If H6 persists, motor replacement.

L Codes (Less Common)

L3 — Compressor Phase Lost

Cause: Missing compressor lead at the contactor or terminal block. Fix: Power down. Inspect compressor terminal connections for corrosion, looseness, or burn marks.

L9 — Power Frequency Out of Range

Cause: Utility power frequency outside 50-60Hz, typically only seen during generator startup or extreme grid disturbance. Fix: Wait for grid to stabilize. If on generator, verify the generator output frequency.

C Codes (Configuration / Communication)

C5 — Jumper Cap Fault

Cause: Outdoor unit jumper cap is missing. Common during install when the cap falls out before the connection is made. Fix: Locate the small jumper cap (looks like a black plastic plug) at the outdoor unit's terminal block. Reseat it firmly.

C4 — Misset Address Pin (Multi-Zone)

Cause: Multiple indoor heads on a multi-zone system share the same address. Fix: Set unique addresses on each indoor head's DIP switches (refer to the install manual for your specific multi-zone system).

U Codes

U8 — Indoor Zero-Crossing Detection Failure

Cause: Indoor control board can't detect AC zero-crossing for inverter timing. Fix: Power cycle. Verify ground connection at indoor unit. If U8 persists, control board replacement.

Multi-Code Strategies

When Multiple Codes Appear Simultaneously

Codes can mask each other. If you're seeing E5 (communication error) along with other codes, fix E5 first — the unit can't reliably report secondary faults until it can communicate.

Codes That Won't Clear After Power Cycle

• F3, F4, F5: protective trips that require fixing the underlying cause
• E7 (after multiple resets): control board replacement
• H6 (after cleaning): motor replacement
• P6 (after coil cleaning): refrigerant work needed

Reset Procedure (When Codes Won't Clear)

1. Turn off power at the breaker
2. Wait 10 minutes
3. Power back on
4. Wait 5 minutes for the unit to complete its self-test
5. Set to Cool mode at 5°F below room temp
6. Observe for 15 minutes

If a code returns within the first 15 minutes, that code is real and needs the corresponding fix. If the unit runs cleanly for 15+ minutes, the original code may have been a transient electrical event (possibly a brownout or surge).

What's Covered Under Warranty

If you're under MrCool's 7-year warranty, error codes that indicate a covered failure (compressor, control board, motor, sensor) qualify for warranty parts replacement. Document the error code, the date it appeared, and any troubleshooting you tried. Then contact MrCool warranty support before any non-trivial repair — unauthorized repairs can void coverage.

For codes related to install errors (C5, C4, P1 from undersized wiring), the warranty doesn't cover the fix because the unit itself isn't faulty. These are install-correction issues.

When to Stop and Call a Pro

Codes that mean stop DIY:

• F3, F4 with persistent recurrence (refrigerant work)
• P6 with persistent recurrence (refrigerant work)
• F5 with immediate recurrence (compressor diagnosis)
• Any code accompanied by burning smell, smoke, or visible damage

For everything else, the steps above will get you 80% of the way to fixing it. Save this article — it's the reference customers come back to.

If your error code isn't on this list (rare but happens with newer models), call (657) 582-0899 and I'll look it up in the latest MrCool service bulletins.

Frequently Asked Questions

How do I clear an error code on a MrCool mini split?

Most codes clear via power cycle: turn off the breaker for 10 minutes, then turn it back on. The unit runs a self-test and clears transient codes. Codes related to active faults (refrigerant pressure, locked compressor, sensor failure) won't clear until the underlying problem is fixed.

What does error code E5 on a MrCool mean?

E5 is a communication error between the indoor and outdoor units. Almost always caused by a wiring issue: loose terminal, damaged 4-conductor control wire, or polarity reversal. Inspect the wire from end to end with power off, reseat all terminals, and verify the wire isn't damaged.

Is error code F4 on a MrCool serious?

Yes — F4 is a low-pressure switch trip that almost always means refrigerant is leaking from the system. Look for oily residue at flare fittings and line joints. Topping off the refrigerant without finding the leak only delays the inevitable repair (and is illegal under EPA Section 608 anyway). Call a licensed HVAC tech to find and fix the leak.

Can I fix MrCool error codes myself?

For sensor faults (E1-E4), wiring issues (E5, E8), and minor mechanical problems (F1, F2, H6 after cleaning), yes — these are homeowner-repairable. For refrigerant pressure trips (F3, F4, F5, P6) and inverter module faults (P0, PA), call a licensed tech. The error code itself tells you whether it's DIY-friendly or pro-only.