MrCool Mini Split Error Codes: E1, EC, P4 and More

By Ray Bennett · Updated 2 October 2026 · 7 min read · Checked against the maker’s manual

MrCool Mini Split Error Codes: E1, EC, P4 and More

Short answer

MrCool uses two sets of codes: E1 and P4 on older DIY units, EL-01 and PC-04 on 4th and 5th Gen. E1 means the indoor and outdoor units are not talking, EC means refrigerant is leaking or missing, and on a new DIY install MrCool's first checks for P4 and P6 are the line set connections and a service valve not fully open. dF, AP, FC and a double dash are not faults at all.

MrCool shows a fault as a code on the air handler’s display, and it uses two sets of them. Older DIY units show short codes like E1 and P4, and 4th and 5th Gen units show longer ones like EL-01 and PC-04. Many owners installed the system themselves, and MrCool’s own first checks for several codes are install mistakes you can put right.

Everything on this page comes from MrCool’s support center: its error code list for each generation, and the troubleshooting article MrCool publishes for each common code. Where MrCool gives a step, this page says so.

Before you start

What to carry: a torch and a pen, and for a new install two wrenches and the hex key for the valves. Ten minutes to read the code, and fifteen with the power off for a reset.

Gas or electric? A mini split is all electric, a heat pump that heats and cools.

Know your generation. MrCool says units before the 4th Gen show P4, and 4th Gen units show PC-04 for the same fault. The code tables below give both.

Reading the code. Most air handlers show it on the front display. MrCool says some models let you call it up with the remote: turn the unit off, then hold the LED or TEMP button for 5 to 10 seconds. The SmartHVAC app shows it on Wi-Fi units.

MrCool's own safety steps. Breaker off for 15 minutes before opening anything. MrCool says to leave the power off that long so the unit is fully de-energized, to use insulated tools, and to wear gloves and safety glasses.

Refrigerant and pressure checks are a professional’s. MrCool says to have a professional check the pressures when a valve or connection check does not clear the code. On 5th Gen units, EH-C1 and EH-C2 mean the built-in refrigerant sensor has detected a leak: switch the system off, open a window and call a technician.

Four codes that are not faults

dF, AP, FC and a double dash are the unit telling you what it is doing. Nothing is broken.

Check 1Free, one minute

Rule these out first

dF: defrost. MrCool says the unit is melting frost off the outdoor coil, a normal part of heating. Frequent defrosts come with humidity, snow on the unit and wind: what a mini split does on heat that looks like a fault.

AP: Wi-Fi pairing. MrCool says the unit is in access point mode, ready to join your home Wi-Fi through the app. It goes once connected.

FC: force cooling. Someone pressed the Force Start button twice. MrCool says it runs cooling for 30 minutes, then switches to auto at 76°F.

A double dash on a multi zone system. MrCool says one zone is set to heat and another to cool. Set every zone to the same mode and avoid auto, then restart the system.

The codes MrCool troubleshoots most

MrCool publishes a troubleshooting article for each of these, and names them in both forms.

Gen 1 to 3	4th and 5th Gen	What MrCool says it means	Check first
E1	EL-01	Indoor and outdoor units not communicating	Wires 1, 2, 3; no splices
E2	EH-02	Zero crossing detection, the indoor board	Power reset
E3	EH-03	Indoor fan speed out of range	The blower wheel spins freely
EC	EL-0C	Refrigerant leak detected, or the system lacks refrigerant	New install: connections and valves
F0	PC-08	Current overload	Power reset, then voltage
F5	EC-07	Outdoor fan speed out of control	The outdoor fan spins freely
P0	PC-00	Inverter module (IPM) protection	Voltage, then a power reset
P1	PC-01	Over or under voltage	Breaker and disconnect
P2	PC-02	Compressor running too hot	Outdoor unit clear and clean
P3	PC-0L	Outdoor temperature too low to run	Wait for warmer weather
P4	PC-04	Inverter compressor drive error	New install: valves and connections
P6	PC-03	Low pressure protection	New install: valves and connections

Two display codes have their own MrCool articles. A flashing 88 with the Wi-Fi symbol usually means wires 2 and 3 are swapped at one end. A solid 88 points at the power supply or the indoor control board.

A new DIY install: the four checks MrCool names

On a new install, MrCool's first checks for EC, P4 and P6 are the refrigerant connections and valves, and for E1 and a flashing 88 the three wires.

Check 2Free, thirty minutes

Check the install, power off first

The line set connections. For EC, P4 and P6, MrCool says to check every connection at the air handler, the condenser and any extension coupler. No threads should show. Tighten with two wrenches, one holding the adapter still.

The service valves. MrCool says both valves at the outdoor unit must be opened all the way to the locking ring. A valve left closed restricts the refrigerant and throws a code.

The king valves on multi zone units. MrCool says the two valves above the normal service connections must be open too, except on 4th Gen dual zone units.

Wires 1, 2 and 3. For E1 and a flashing 88, MrCool says the cable must run in the same order at both ends with no splices. On DIY systems MrCool gives red to 1, white to 2 and black to 3.

Multi zone wiring by port. For P4 on a new multi zone system, MrCool says each air handler’s wires must match its refrigerant ports: the head on the A lines wires to 1A, 2A and 3A.

The checks for a system that was working

Check 3Free, twenty minutes

Work the owner checks

The 15 minute reset. For E2, F0, P2 and a solid 88, MrCool’s first step is the breaker off for 15 minutes, then back on.

The indoor fan, E3 and EH-03. With the power off, MrCool says to look for debris in the blower wheel and spin it by hand. It should turn freely.

The outdoor fan, F5 and EC-07. MrCool says to clear anything around the outdoor fan and spin it by hand, power off. It should move without resistance.

The outdoor unit, P2 and PC-02. MrCool names restricted airflow and a dirty coil. Clear debris and rinse the coil: how to rinse an outdoor coil without bending the fins.

The cold, P3 and PC-0L. MrCool says the unit stops below -13°F to protect itself and clears when it warms. If it is warmer than that, check the outdoor air sensor on the back of the unit is not buried in ice or snow.

After a storm, E1. MrCool’s checks on an existing install start with power surges, storms and physical damage such as loose wires, burn marks or pests.

The other codes in MrCool’s list

These are sensor and board faults, which MrCool lists by generation. They are technician work once a reset has not cleared them.

What MrCool says it means	Gen 1 to 3	4th and 5th Gen
Indoor unit memory (EEPROM)	E0	EH-00, EH-0A
Indoor room temperature sensor	E4	EH-60
Indoor coil temperature sensor	E5	EH-61
Outdoor air temperature sensor	F1	EC-53
Condenser coil temperature sensor	F2	EC-52
Compressor discharge temperature sensor	F3	EC-54
Outdoor unit memory (EEPROM)	F4	EC-51
Evaporator outlet temperature sensor	None	EC-56
Indoor board and display board not talking	None	EH-0b
Outdoor main chip and driver chip not talking	None	PC-40
Smart kit not installed	P7	None

When it needs a technician

Check 4

Know when to stop

EC or EL-0C on a system that was working. MrCool says that on an existing install it points in most cases to a low refrigerant charge. A technician needs to find the leak: signs the refrigerant is leaking.

P4 or PC-04 with oily residue. MrCool says to look for oil on the lines, the insulation or the unit. Oil marks a leak, and MrCool says the system may need a technician to top up the charge.

P6 or PC-03 that the valve checks did not clear. MrCool names restrictions or a low charge, and says a professional should check the pressures.

P0, F0 and P1 with abnormal voltage or burn marks. MrCool’s next steps are voltage readings at the terminals and a look at the outdoor board. That is meter work at full voltage.

Anything with burn marks on a board. MrCool asks for photos of them, and says a board with burnt areas may need replacing.

Questions people ask

What does E1 mean on a MrCool mini split?

The indoor and outdoor units are not communicating. On 4th and 5th Gen units it shows as EL-01. MrCool’s first checks are the three wires, their order at both ends and no splices, then the power supply.

What is the EC code on MrCool?

Refrigerant leak detection. On a new install, MrCool says to check the line set connections and that both valves are fully open. On a system that was working, it usually means a low charge, which needs a technician.

What does dF mean on a MrCool?

Defrost. MrCool says it is a normal part of heating and the unit returns to heat by itself. Keep snow off the outdoor unit.

Why does my MrCool say AP?

It is in Wi-Fi pairing mode, ready to connect through the MrCool app. MrCool says the code disappears once the unit joins your network.

What does a flashing 88 mean?

With the Wi-Fi symbol, MrCool says it is usually a wiring mistake, most often wires 2 and 3 swapped at one end. A solid 88 points at the power supply or the indoor control board.

What is PC03 on a MrCool?

Low pressure protection, shown as P6 on older units. On a new install, check the connections and that every valve is fully open. Otherwise it needs a professional to check the pressures.

Sources: MrCool support center: "Mini Split Systems Error Codes" and MrCool's troubleshooting articles for each code (updated October 2025 to August 2026)