Mitsubishi Electric fault codes

Likely causes, most common first

1. Indoor/outdoor connecting wire loose, disconnected or wired to the wrong terminals
2. Power to the outdoor unit is off or its breaker is tripped
3. Defective indoor or outdoor electronic control P.C. board

What you can safely check yourself

• Check that the breaker feeding the outdoor unit is on and has not tripped
• Turn the system off at the breaker, wait one minute, and turn it back on once
• Check that the outdoor unit is running and not iced over or blocked by snow or debris

Likely causes, most common first

1. Indoor coil thermistor or room temperature thermistor out of its resistance range (defective)
2. Thermistor connector loose or not fully seated on the indoor control board
3. Broken or pinched thermistor lead wire

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once to see if the code clears

Likely causes, most common first

1. Something is physically blocking the line-flow fan wheel from turning
2. Defective indoor fan motor
3. Defective indoor electronic control P.C. board
4. Loose fan motor connector

What you can safely check yourself

• Turn the system off at the breaker and check that nothing has fallen into the indoor unit air outlet
• Remove and clean the air filters
• Restore power at the breaker once and see if the fan starts

Likely causes, most common first

1. Defective indoor electronic control P.C. board

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Outdoor unit service (stop) valve closed or not fully open
2. Compressor connecting wire loose, disconnected or reversed
3. Defective compressor or inverter P.C. board
4. Low supply voltage

What you can safely check yourself

• Check that the outdoor unit is clear of snow, ice, leaves and debris and has open air space around it
• Check that the breaker feeding the outdoor unit is on and not tripped
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Defective outdoor thermistor (discharge, defrost, ambient, fin or heat-exchanger sensor)
2. Thermistor connector loose on the outdoor control board
3. Broken thermistor lead wire

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Defective inverter P.C. board
2. Defective outdoor electronic control P.C. board

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Outdoor unit stop valve closed or not fully open
2. 4-way reversing valve not operating properly
3. Some other outdoor fault that must be read with the failure mode recall function

What you can safely check yourself

• Check that the outdoor unit is clear of snow, ice and debris
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Defective inverter P.C. board
2. Defective outdoor electronic control P.C. board

What you can safely check yourself

• Check that the breaker feeding the outdoor unit is on and not tripped
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. One indoor unit set to COOL or DRY while another on the same outdoor unit is set to HEAT

What you can safely check yourself

• Set every indoor unit on the system to the same mode (all cooling, or all heating)
• Check the mode setting on each remote, including any room you are not using
• Note that DRY counts as cooling for this purpose

Likely causes, most common first

1. Defective thermistor characteristics
2. Contact failure of connector CN20 on the indoor controller board (insert failure)
3. Breaking of wire or contact failure of thermistor wiring
4. Defective indoor controller board

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once to see if it resets

Likely causes, most common first

1. Defective thermistor characteristics
2. Contact failure of connector CN44 on the indoor controller board (insert failure)
3. Breaking of wire or contact failure of thermistor wiring
4. Defective refrigerant circuit driving the thermistor to 194F or more or -40F or less
5. Defective indoor controller board

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once to see if it resets

Likely causes, most common first

1. Contact failure of the float switch connector (insert failure)
2. Float switch connector disconnected
3. Defective indoor controller board

What you can safely check yourself

• Check the condensate drain line outside for a clog, kink or blockage
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Malfunction of the drain pump
2. Defective drainage - clogged drain pump or clogged drain pipe
3. Defective drain float switch, or the float caught on a moving part
4. Defective indoor controller board

What you can safely check yourself

• Check the condensate drain line outside for a clog, kink, ice or debris
• Check the air filters and clean them, since a dirty filter can make condensate ripple onto the float switch
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Clogged filter reducing airflow
2. Short cycle of the air path - supply air blowing straight back into the return
3. Low-load (cooling) or overload (heating) operation outside the tolerance range
4. Defective indoor fan motor
5. Defective outdoor fan control
6. Overcharge of refrigerant
7. Defective (clogged) refrigerant circuit

What you can safely check yourself

• Remove and clean or replace the air filters - the manual's first listed check is 'Check clogs of the filter'
• Remove anything blocking the indoor unit air inlet or outlet, including furniture, curtains and boxes
• Check that the outdoor unit is clear of snow, ice, leaves and debris
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Only a slight temperature difference between room air and pipe temperature - shortage of refrigerant, thermistor holder fallen off the pipe, or a defective refrigerant circuit
2. Reverse connection of the extension pipe (on multi-unit installations)
3. Reverse wiring of the indoor/outdoor connecting wire (on multi-unit installations)
4. Defective detection by the room and pipe temperature thermistors
5. Stop valve is not opened completely

What you can safely check yourself

• Check that the outdoor unit is clear of snow, ice and debris
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Defective thermistor characteristics
2. Contact failure of connector CN44 on the indoor controller board (insert failure)
3. Breaking of wire or contact failure of thermistor wiring
4. Thermistor driven past 194F or below -40F by a defective refrigerant circuit
5. Defective indoor controller board

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once to see if it resets

Likely causes, most common first

1. Drain pump trouble
2. Defective drainage - drain pump clogging or drain pipe clogging
3. Open circuit of the float switch
4. Contact failure of the float switch connector
5. Dew condensation on the float switch, or drain water rippling because of a clogged filter
6. Extension piping or connecting-wire mismatch on twin/triple/quadruple systems

What you can safely check yourself

• Check the condensate drain line outside for a clog, kink, ice or debris
• Remove and clean or replace the air filters - the manual lists filter clogging as a cause of the float switch tripping
• Turn the system off at the breaker, wait one minute, and turn it back on once, since the manual says the abnormality is only released by resetting main power

Likely causes, most common first

1. Abnormal operation of the 4-way (reversing) valve
2. Disconnection of or leakage in refrigerant pipes
3. Air in the refrigerant piping
4. Indoor fan not rotating - defective fan motor or defective indoor control board
5. Defective (clogged) refrigerant circuit

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once, since the manual says the error stays latched until the power source is reset

Likely causes, most common first

1. Contact failure at the transmission wire of the remote controller
2. All remote controllers are set as 'sub' - in that case E0 shows on the remote and E4 shows on the outdoor board LEDs
3. Miswiring of the remote controller
4. Defective transmitting/receiving circuit of the remote controller or indoor controller board
5. Noise on the remote controller transmission wire

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Defective remote controller

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Defective remote controller

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Two remote controllers are both set as 'main'
2. One remote controller is connected to 2 or more indoor units
3. Repetition of refrigerant address
4. Defective transmitting/receiving circuit of the remote controller or the indoor controller board
5. Noise has entered the remote controller transmission wire

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Contact failure at the remote controller transmission wire
2. All remote controllers set as 'sub'
3. Miswiring of the remote controller
4. Defective transmitting/receiving circuit of the remote controller or indoor controller board
5. Noise on the remote controller transmission wire

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Two remote controllers both set as 'main'
2. One remote controller connected to 2 or more indoor units
3. Repetition of refrigerant address
4. Defective transmitting/receiving circuit of the indoor controller board or remote controller
5. Noise has entered the remote controller transmission wire

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Contact failure, short circuit or miswiring (reverse wiring) of the indoor/outdoor unit connecting wire
2. Defective transmitting/receiving circuit of the indoor controller board
3. Defective transmitting/receiving circuit of the outdoor controller board
4. Noise has entered the indoor/outdoor unit connecting wire

What you can safely check yourself

• Check that the breaker feeding the outdoor unit is on and has not tripped
• Check that the outdoor unit is clear of snow, ice and debris and that nothing has damaged the wire cover
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Defective transmitting/receiving circuit of the indoor controller board
2. Noise has entered the power supply
3. Noise has entered the outdoor control wire

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Indoor/outdoor unit connecting wire has contact failure or is miswired
2. Defective communication circuit of the outdoor controller board
3. Defective communication circuit of the indoor controller board
4. Noise has entered the power supply or the indoor/outdoor connecting wire

What you can safely check yourself

• Check that the breaker feeding the outdoor unit is on and has not tripped
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Indoor/outdoor unit connecting wire has contact failure or is miswired
2. Defective communication circuit of the outdoor controller board
3. Defective communication circuit of the indoor controller board
4. Noise has entered the power supply or the indoor/outdoor connecting wire

What you can safely check yourself

• Check that the breaker feeding the outdoor unit is on and has not tripped
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Contact failure or miswiring of the indoor/outdoor unit connecting wire
2. Connecting wire diameter or length is outside the specified capacity (total wiring length limit 80 m)
3. Too many indoor units connected to one outdoor unit (4 units or more)
4. Defective transmitting/receiving circuit on the outdoor or indoor controller board
5. Two or more outdoor units set to refrigerant address 0
6. Noise on the power supply or connecting wire

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Contact failure or miswiring of the indoor/outdoor unit connecting wire
2. Connecting wire diameter or length is outside the specified capacity
3. Defective transmitting/receiving circuit on the outdoor or indoor controller board
4. Two or more outdoor units set to refrigerant address 0 in a group control system
5. Noise on the power supply or connecting wire

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Contact failure of the indoor/outdoor unit connecting wire
2. Connecting wire diameter or length is outside the specified capacity
3. Two or more outdoor units set to refrigerant address 0 in a group control system
4. Noise on the power supply or connecting wire

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Breaking of wire or contact failure of connector CN2 between the outdoor controller board and the outdoor power circuit board
2. Breaking of wire or contact failure of connector CN4 between the same two boards
3. Defective communication circuit of the outdoor power circuit board
4. Defective communication circuit of the outdoor controller circuit board

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Indoor unit model and outdoor unit model are not a permitted combination
2. Wrong indoor unit connected during a replacement

Likely causes, most common first

1. Noise has entered the remote controller transmission wire
2. Noise has entered the indoor/outdoor unit connecting wire
3. Outdoor unit is not an inverter model

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Defective indoor controller board

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. 63L connector disconnected or has contact failure on the outdoor controller board
2. 63L low pressure switch itself has failed or is tripped
3. Defective outdoor controller circuit board

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Disconnection or contact failure of the 63H connector on the outdoor controller circuit board
2. Disconnection or contact failure at the 63H switch itself
3. 63H is working (tripped) because of defective parts
4. Defective outdoor controller circuit board

What you can safely check yourself

• Check that the outdoor unit is clear of snow, ice, leaves and debris so it can reject heat
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Short cycle of the indoor unit - supply air recirculating back into the return
2. Clogged filter on the indoor unit
3. Decreased airflow from a dirty indoor fan or dirty indoor heat exchanger
4. Locked or malfunctioning indoor fan motor
5. Stop valve not fully open
6. Clogged or broken pipe
7. Locked or malfunctioning outdoor fan motor
8. Short cycle of the outdoor unit or dirty outdoor heat exchanger
9. Disconnection or contact failure of the 63H connector on the outdoor controller board

What you can safely check yourself

• Remove and clean or replace the indoor air filters
• Clear anything blocking the indoor unit inlet or outlet
• Check the outdoor unit is clear of snow, ice, leaves, grass clippings and stacked items, with open space all around
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Shortage of refrigerant
2. Defective operation of the stop valve (not fully open)
3. Defective action of the linear expansion valve
4. Clogging with foreign objects in the refrigerant circuit
5. Defective discharge or compressor-surface thermistor
6. Defective outdoor controller board

What you can safely check yourself

• Check the outdoor unit is clear of snow, ice and debris
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Disconnection or contact failure of connectors TH4 or TH33 on the outdoor controller circuit board
2. Defective thermistor
3. Defective outdoor controller circuit board

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Disconnection or contact failure of the thermistor connectors on the outdoor controller circuit board or connector CN6 on the outdoor power circuit board
2. Defective thermistor
3. Defective outdoor controller circuit board

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. The outdoor fan motor is not running
2. Failure of the outdoor fan
3. Airflow path is clogged
4. Rise of ambient temperature around the outdoor unit
5. Defective thermistor
6. Defective input circuit on the outdoor power circuit board

What you can safely check yourself

• Check that the outdoor unit has clear air space around it and is not blocked by fencing, plants, stored items, snow or leaves
• Check that the outdoor fan is spinning when the unit runs
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Outdoor stop valve is closed
2. Decrease of power supply voltage
3. Looseness, disconnection or reversed connection of the compressor wiring
4. Defective compressor
5. Defective outdoor power circuit board

What you can safely check yourself

• Check that the breaker feeding the outdoor unit is on and has not tripped
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Disconnection or loose connection of the discharge temperature thermistor (TH4)
2. Defective high pressure or temperature sensing
3. Disconnection or loose connection of the linear expansion valve or its connector
4. Defective linear expansion valve
5. Overcharge of refrigerant

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Failure in the outdoor DC fan motor
2. Failure in the outdoor controller board

What you can safely check yourself

• Turn the power off at the breaker first, then look for leaves, ice, a stick or other debris jamming the outdoor fan blade
• Clear snow and ice from around and on top of the outdoor unit
• Turn the system back on at the breaker once

Likely causes, most common first

1. Abnormal increase in power source voltage
2. Decrease in power source voltage or an instantaneous drop
3. Disconnection or loose connection of the compressor wiring
4. Misconnection of the reactor (DCL)
5. Defective outdoor power circuit board
6. Defective reactor (DCL)
7. Disconnection or loose connection of CN2 between the outdoor power board and the controller board

What you can safely check yourself

• Check whether the house has had a power flicker, brownout or storm outage recently
• Check that the breaker feeding the outdoor unit is on and has not tripped
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Defective outdoor fan (fan motor), or short cycle of the outdoor unit during cooling operation
2. Defective outdoor pipe thermistor (TH3) or condensing temperature sensor
3. Defective outdoor controller board

What you can safely check yourself

• Check that the outdoor unit is clear of snow, ice, leaves and stored items and has open air space around it
• Check that the outdoor fan is spinning when the unit runs
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Disconnection or contact failure of connector 63HS on the outdoor controller board
2. Defective pressure sensor
3. Defective outdoor controller circuit board

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Stop valve is closed
2. Decrease of power supply voltage
3. Looseness, disconnection or reversed connection of the compressor wiring
4. Defective compressor
5. Defective outdoor power circuit board
6. DIP switch setting difference on the outdoor controller circuit board

What you can safely check yourself

• Check that the breaker feeding the outdoor unit is on and has not tripped
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Defective current sensor circuit on the outdoor power circuit board
2. Decrease of power supply voltage

What you can safely check yourself

• Check that the breaker feeding the outdoor unit is on and has not tripped
• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Stop valve of the outdoor unit is closed during operation
2. Leakage or shortage of refrigerant
3. Malfunction of the linear expansion valve

What you can safely check yourself

• Turn the system off at the breaker, wait one minute, and turn it back on once

Likely causes, most common first

1. Stop valve is closed
2. Decrease of power supply voltage
3. Looseness, disconnection or reversed connection of the compressor wiring
4. Defective fan on the indoor or outdoor units
5. Short cycle on the indoor or outdoor units
6. Defective indoor or outdoor coil
7. Defective compressor
8. Defective outdoor power circuit board
9. DIP switch setting difference on the outdoor controller board

What you can safely check yourself

• Remove and clean or replace the indoor air filters
• Check that the outdoor unit is clear of snow, ice, leaves and stored items
• Clear anything blocking the indoor unit inlet or outlet
• Turn the system off at the breaker, wait one minute, and turn it back on once