Mitsubishi Electric City Multi Air Conditioning Systems

This error indicates a problem with the serial communication within the outdoor unit. It can be caused by broken wires, poor connector contact, or malfunctions in the communication circuits on either the outdoor controller board or power board.

This error indicates that the compressor is operating at an abnormally high temperature. Causes can include issues with stop valves, refrigerant shortage, defective sensors, or blockages in the refrigerant system.

This error signifies an abnormally high pressure in the system. This can be caused by various factors, including closed valves, clogged pipes or filters, malfunctioning fans, dirty heat exchangers, or sensor issues.

This error indicates an issue with superheat due to an abnormally low discharge temperature. This can be caused by problems with the TH4 sensor, its holder, or issues with the LEV (Linear Expansion Valve) coil or connector.

This error specifically occurs in cooling mode and indicates that an outdoor liquid or gas valve is closed, or the outdoor LEV (Linear Expansion Valve) is malfunctioning, causing a blockage.

This error indicates a low refrigerant level in the system. This can be caused by stop valves not fully open, defective sensors, or actual gas leakage.

This error indicates that the freeze protection mechanism for the branch box or indoor unit has been activated. This can be caused by incorrect piping, miswiring of units or LEVs, or a malfunction of the LEV.

This error indicates a problem with the 4-way valve, specifically when the system is operating in heating mode. This critical component directs refrigerant flow for heating and cooling, and a fault can arise from valve failure, coil issues, or wiring problems.

This error indicates that water leakage has been detected within the indoor unit. This is often caused by a blocked drain, a faulty drain pump, or a damaged drain pan.

This error means the drain overflow protection system has been activated, indicating that the condensate drain pan is full or overflowing. This is usually due to a clogged drain line or a malfunctioning drain pump.

This error indicates a problem with the drain sensor, which monitors the water level in the condensate drain pan. A faulty sensor might lead to the system incorrectly detecting an overflow or not detecting one when it occurs.

This is a broad power supply error indicating voltage fluctuations (too low or too high), an open phase, or a problem with the power synchronization signal. It can stem from issues with the main power supply or internal electrical components.

This error indicates an issue with the heat sink temperature in the outdoor unit. It could be caused by blockages in the fan or airflow path, a faulty fan motor, high ambient temperatures, or a defective temperature sensor.

This is a serious electrical fault indicating a problem with the Inverter Power Module (IPM), specifically a short-circuit or ground fault. It can also point to overcurrent issues due to a short-circuited motor.

This error signifies a problem with the power module or an overcurrent condition. This is a critical electrical fault that can be caused by short-circuited wiring, a faulty compressor, or a defective outdoor power circuit board.

This error indicates an overcurrent condition caused by a short-circuited motor within the system, likely associated with the Inverter Power Module (IPM). It's a critical electrical fault requiring immediate attention.

This fault signifies an instantaneous overcurrent or a sustained overcurrent (effective value) detected by the system's software. It points to a severe electrical issue often linked to the Inverter Power Module (IPM).

This error indicates a problem with the outdoor unit's fan. It could be due to a malfunctioning fan motor, a disconnected fan connector, or a defective outdoor multi controller circuit board.

This error indicates a problem with the return air temperature sensor (TH21) in the indoor unit. It could be due to a faulty thermistor or a bad connection, leading to incorrect temperature readings for the return air.

This code indicates an issue with the air inlet thermistor (TH21) or the compressor temperature thermistor (TH4) in the outdoor unit. It suggests that the thermistor circuit is either disconnected or shorted, impacting temperature readings.

This fault signals an issue with the indoor unit's pipe temperature sensor (TH22). A defective thermistor or a connection problem can cause this, resulting in inaccurate pipe temperature readings.

This code signifies a problem with the liquid pipe temperature thermistor (TH22) or the suction pipe temperature thermistor (TH6) in the outdoor unit. It indicates an open or short circuit in the thermistor's wiring or component, leading to incorrect temperature readings.

This error indicates a problem with the indoor unit's gas-side pipe temperature sensor (TH23). This could be due to a faulty thermistor or a loose connection, leading to inaccurate temperature readings for the gas pipe.

This code indicates an open or short circuit condition with the gas pipe temperature thermistor (TH23). This thermistor monitors the temperature of the gas pipe in the outdoor unit and is crucial for system operation.

This fault refers to a problem with the outside temperature sensor (TH24) for the indoor unit. A defective thermistor or a loose connection can cause this, leading to incorrect outdoor temperature readings for the indoor unit's control.

This error pertains to the temperature sensor (TH6) that monitors the HIC circuit outlet. The sensor might be short-circuited or open, leading to inaccurate temperature readings for this critical part of the system.

This fault indicates a problem with the outdoor temperature sensor (TH7). The sensor could be short-circuited or open, providing incorrect environmental temperature data to the system.

This fault indicates a problem with the heatsink temperature sensor (THHS). This sensor is crucial for monitoring the temperature of the heatsink during backup operation. If the issue recurs after a reset, the INV board may need replacement.

This fault indicates an issue with the heat sink temperature thermistor (TH8) in the outdoor unit. The thermistor might have a broken connection, a faulty characteristic, or there's a problem with the circuit board.

This error points to an issue with the temperature sensor (TH15) located at the bottom of the compressor shell. The sensor might be short-circuited or open, leading to inaccurate temperature readings for the compressor.

This fault indicates a problem with the high-pressure sensor (63HS1). This sensor measures the high-side refrigerant pressure, and a fault here suggests an issue with the sensor itself or the pressure readings.

This error indicates a problem with the high pressure sensor in the outdoor unit. Causes can range from a defective sensor, gas leakage leading to pressure drop, or issues with connections or the circuit board.

This error points to a problem with the low pressure sensor in the outdoor unit. It could be due to a faulty sensor, refrigerant leakage causing pressure drop, or issues with connections or the circuit board.

This fault indicates an issue with the current sensor. Possible causes include problems with the power supply voltage, compressor wiring, or a faulty input sensor on the outdoor power circuit board.

This fault indicates a problem with the ACCT (Alternating Current Current Transformer) sensor circuit during backup operation. It can be caused by an open circuit, a loose ACCT connector, or faulty ACCT wiring.

This error indicates a problem with the current sensor during backup operation. This typically means there is an issue with the sensor's circuit, or components like the fan inverter board or outdoor fan itself are faulty.

This error indicates a problem with the current sensor during backup operation. This typically means there is an issue with the sensor's circuit, or components like the fan inverter board or outdoor fan itself are faulty.

This error means there's a problem with the drain float switch in the indoor unit. This switch detects water levels in the drain pan, and a contact failure suggests it's not working correctly, possibly due to a blockage or a faulty switch.

This error indicates that two or more units (such as outdoor, indoor, Fresh Master, Lossnay, or remote controllers) within the air conditioning system have been assigned the same address. This prevents proper communication.

This error indicates that two or more units (outdoor, indoor, Fresh Master, Lossnay, or remote controller) in the system have been assigned the same address. This can also be caused by noise interference.

This fault suggests an issue with the transmission processor hardware, often due to data collisions during wiring changes or polarity changes while the power is on. It can also be caused by a faulty transmission circuit or noise interference.

This error signifies that the transmission processor is unable to transmit data because the transmission line is busy. This can be caused by short-cycle voltage noise, an increased amount of transmission data due to miswiring, or a malfunction in a repeater.

This error indicates a problem with signal communication to the transmission processor. It's often caused by accidental disturbances like noise or lightning, or a hardware malfunction in the transmission processor.

This error means that a unit did not receive an acknowledgment signal from another unit. This can happen if an indoor unit's address was changed during operation, if transmission wiring is faulty, or due to a controller failure.

This 'No ACK' error means the system cannot recognize the controller associated with a specific address. This typically happens if an address switch was changed while power was on, or if Fresh Master/Lossnay addresses were changed after synchronization.

This error indicates that there's a continuous failure in data transmission, meaning the system is not receiving a response 'frame' or packet. This can be caused by continuous noise, a decline in transmission voltage/signal due to line issues, or a malfunction in the error source controller.

This error indicates that the outdoor unit, indoor unit, or remote controller is not receiving a communication signal. This can be caused by wiring issues, noise interference, or a problem with the sending/receiving circuit.

This fault indicates that there's an issue with the MA communication, specifically related to receiving signals. It can occur due to problems with wiring or remote controller circuit malfunctions.

This error occurs when the total capacity of all connected indoor units exceeds the system's specified limit. It can also be triggered by incorrect registration of the outdoor unit's model name.

This error indicates that an indoor unit connected to the system is not compatible. The system has specific model code ranges for connectable indoor units, and this error appears if a connected unit falls outside these ranges.

This error signifies a problem with the system's MA communication, specifically when trying to send signals. It can be due to multiple main remote controllers, circuit malfunctions, or noise.