MITSUBISHI ELECTRIC HEAT PUMP & DUCTLESS SYSTEM REPAIR

The problem arises when there is a communication issue between the PCBs (Printed Circuit Boards) in the outdoor unit. If the model number is YGMA, YHMA, YJMA, YKMA, or YLMA, the communication issue may occur between the main board and the inverter board or between the main board and the fan board.

The test operation dip switch on the Lossnay circuit board has been set ON.

Inadequate cooling of the compressor can result from insufficient refrigerant levels or a blockage in the refrigerant circuit, elevated ambient temperatures during operation, or airflow issues in either the indoor or outdoor unit (depending on the operational mode). Additionally, compressor overheating may occur due to heightened friction, indicating the onset of compressor seizing, or inaccurate thermistor readings.

There is a possible refrigerant leak. Restriction or blockage in refrigerant circuit causing low side pressure to drop. Problem with the pressure sensor is reading incorrectly.

High-pressure faults are mostly caused by a blocked condenser coil, a faulty fan motor, a restriction of airflow on indoor units in heating mode or a blockage/restriction in the pipework.

Typically brought about by an excess of refrigerant returning to the outdoor unit, leading to overcooling of the compressor. This issue arises when the system is either overcharged, or there are malfunctions in the valves, allowing refrigerant to “flood” back to the compressor.

The water pump is off/faulty. The water flow rate is too slow. The float switch is faulty.

Inspect the indoor drip tray for water accumulation. If there is an excess of water, it suggests a potential problem with the internal pump or drains. Conversely, if the tray is dry or lacks sufficient water to raise the float switch, assess the float switch for continuity. When the switch is lifted, the circuit should be closed, and if the switch is down, the circuit should be open.

The drain sensor is open/short-circuit.

Missing main phase. Check the power supply and noise filter for the correct 3 phase, and check wiring and fuses.

Transmission (M-Net), incorrect wiring. Check wiring, high current, and incorrect voltage on the transmission line and/or M-Net board. Make sure M-net transmission wiring is daisy-chained.

Incorrect power supply, blown fuses or possible faulty PCB. Check mains power is correct, check the fuses, and connections PCB.

Inspect the fan motors for potential connection issues if a faulty connection of a fan is suspected. Examine the leads between the Control board and the Power board for any faults if there’s a faulty connection in the leads. Confirm the correct setting of the model selection switch (SW6) to match the designated model. In environments with high ambient temperatures, check the temperature around the Lossnay unit. Ensure that the fan motors are securely fixed in place for proper installation. Examine the centrifugal fan to ensure it is free of deformities or obstructions. If foreign objects are affecting the centrifugal fan, consider replacing the fan motor. In the case of a malfunctioning fan motor, replacing the circuit board may be necessary. Investigate the connections of the reactor (TB3-4) and check its resistance to address circuit board issues. To pinpoint the specific fan with an issue, refer to the LED flashing sequence and seek assistance from After Sales Technical Support.

Low mains power supply, diode fault. Check mains supply. Check DC bus voltage coming from the diode.

Incorrect mains supply or fan board fault. Check mains power is ok and there is at least 300vdc at the diode stack.

Blockage in the air passage of inverter heatsink, Inverter board failure, inverter fan failure. Check blockages in air duct failure of INV fan or failure of the thermistor.

If a high current is detected for more than 10mins. Check inverter balance. Reduced airflow through the heat sink.

Elevated amperage is being drawn by the compressor, or there may be a problem with the inverter. Conduct an inverter output test to assess the proper functioning of the inverter. Refer to the “Inverter Testing Guide” in the City Multi section of the APP for guidance. If the inverter proves to be functioning correctly, proceed to inspect the compressor windings for any short or open circuits.

Grounding fault of fan motor or fan board fault. Check the voltage on CNVDC on the fan. This should be a high DC voltage around 580vdc. Also check the fan motor windings for an open or short circuit.

Reduced airflow through the heat sink. Fan motor problem. THHS thermistor problem.

Malfunctioning Thermistor – Dead Short/Open Circuit: This issue may be associated with either indoor or outdoor components, so initially, consult the fault code to identify the unit in fault. If a damaged thermistor cable or a poor connection to the PCB is suspected, inspect the connection of the thermistor on the PCB and assess the thermistor wiring. In cases where the PCB is incorrectly reading the thermistor value, unplug the thermistor and test the resistance value to troubleshoot the problem.

The circuit board cannot read the thermistor correctly. Check the connection onto the circuit board, check the resistance of the thermistor, replace the thermistor, replace the circuit board.

Reduced airflow through inverter heatsink. Open/short circuit sensor, disconnected from PCB.

PS1 Pressure fault. Check pressure reading using the dipswitches outdoor. Check the connection of PS3 on PCB.

ACCT or DCCT sensor error. Check inverter error details, check the resistance of the current sensor, and check the connections of sensors.

The indoor unit’s internal float switch connector has detected an open circuit. Check the float switch is operating correctly. If the switch is down then the switch should be open. Also, check for external pumps wired in across the fail-safe connection.

The remote controller is faulty, replace the controller.

Multiple units share the same MNET address, or two or more devices are assigned identical addresses. Examine the address configuration of each device within the MNET network. Additionally, verify the address settings on outdoor units, indoor units, BC boxes, and remote controllers to identify and rectify instances where duplicate addresses are present.

No voltage or short circuit on M-Net transmission line TB7. Check TB7 connections on outdoors and central controllers. Check for voltage on TB7. Check cable size and spec.

Interference in sound transmission. Polarity issue on TB7: Examine the M-Net connection on TB7 and the central controller, checking the cable size and specifications. If the error initially occurred on a specific controller, assess and replace it if necessary. In the event of a faulty Lossnay circuit board, proceed to replace the circuit board.

Power is supplied to the same transmission cable from two or more power supply units, the power supply unit is connected to the TB3 side of the power supply expansion units, or the power supply units are connected to the indoor and outdoor transmission cables.

Poor connection of MNET terminals, MNET cables have been terminated whilst the unit is powered, or malfunction of the unit PCB.

Lossnay has no power, or the lossnay address has been changed. The transmission cable is in excess of 500m or is not securely terminated.

In instances involving multiple Lossnay units, potential issues may arise if the Main/Sub switch is not appropriately set, there is interference on the transmission line, the cable length exceeds 500m, the transmission cable is not securely connected, or a multi-core cable is utilized for various purposes, leading to interference.

MA controller being wired into the M-Net. Wrong cable size/spec. Check where the remote is wired to, check cable length is no bigger than 500 meters, check the connection and type of cable used, and check R/C is not set Sub on field settings.

MA controller being wired into the M-Net. Wrong cable size/spec. Check where the remote is wired to, check cable length is no bigger than 500 meters, check the connection and type of cable used, and check R/C is not set Sub on field settings.

MA controller being wired into the M-Net. Wrong cable size/spec. Check where the remote is wired to, check cable length is no bigger than 500 meters, check the connection and type of cable used, and check R/C is not set Sub on field settings.

MA controller being wired into the M-Net instead of the remote terminals. Wrong cable size/spec. Check where the remote is wired to, check the cable length is no bigger than 500 meters, check the connection and type of cable being used, and check R/C is not set Sub on field settings.

The total indoor unit capacity exceeds the outdoor unit allowable capacity. On a PURY outdoor you are allowed up to 150% of its capacity and on a PUHY/PUMY outdoor you can have up to 130% of its capacity.

SW2 set wrong on indoors, SW5 dips set wrong on YHM-A outdoor, SW3-10 on older kit.

The outdoor unit is not seeing any indoor units or it is seeing more than the allowable value. Check voltage on M-Net, power to the BC box, check dip switches are set correctly on the BC box and the model type of BC box is correct for the system.

GUF unit being used on City Multi system. Make sure SW3-1 setting is on, on the GUF.

Loose or miss wiring of TB3 or TB7. SW5 dip 7 is not set outdoors. The transmission booster was turned off. Check M-Net connections, and dipswitches outdoors.

More than 1 unit in the group is set to as the Main Lossnay (SW5-10 ON), or the group contains two or more units with the same address. The Lossnay that is set to the Main, has not been set to the lowest unit address in the group.

SW5 set wrong on the outdoor or wrong resistors fitted. Check dips, resistors and thermistors.

Check split with MAC 399 wired onto the TB5 line, not the TB7. Check M-Net wiring on systems.

A malfunctioning controller or inadequate wiring connection, along with abnormal voltage reaching the remote controller, may be the cause. Examine the wiring connection from the remote controller to the FTC terminals, ensuring a 12VDC supply to the remote controller. Confirm the illumination of LED2 on the FTC Control board to verify proper functioning.

Incorrect wiring of remote or incorrect dip switch setting if units are grouped. Check unit addressing if grouped or check remote is only wired to the master indoor unit.

Incorrect settings on SW1 switches at the outdoor unit or poor connection or wiring of the remote controller. Check for 12vdc down to the controller and make sure LED 2 is lit on the FTC board, also check the SW1 dips switches on the outdoor unit are set correctly.

Incorrect wiring of the remote controller, insufficient 12VDC supply to the controller, or incorrect settings on the SW1 switches at the outdoor unit could be the issue. Verify the presence of a 12VDC supply to the controller and ensure the illumination of LED 2 on the FTC board. Additionally, examine the SW1 dip switches on the outdoor unit to confirm they are set correctly.

Communication loss or absence between the FTC and outdoor Ecodan may result from an inadequate connection of the interconnecting cable or an incorrect 12-24VDC fluctuating voltage between S2 and S3. To address this, reset the power supply to both the indoor FTC and outdoor Ecodan. Restore power to the indoor unit first, followed by the outdoor unit. Examine the connections and voltages of the interconnecting cable. Additionally, inspect the LEDs on the indoor FTC for any anomalies.

Mis-wiring of indoor to outdoor cable. The system powered up incorrectly. Check for pumps wired in, Check the indoor isolator, and Repower in the correct sequence i.e. indoor then outdoor.

Communication loss or absence between the FTC and the outdoor Ecodan may be attributed to an insufficient connection of the interconnecting cable or an incorrect fluctuating voltage of 12-24VDC between S2 and S3. To address this issue, initiate a power supply reset for both the indoor FTC and outdoor Ecodan. Restart the indoor unit first, followed by the outdoor unit. Inspect the interconnecting cable for secure connections and appropriate voltages. Additionally, assess the LEDs on the indoor FTC for any irregularities.

Communication loss or absence between the FTC and the outdoor Ecodan may result from a suboptimal connection of the interconnecting cable or an incorrect fluctuating voltage of 12-24VDC between S2 and S3. Additionally, if independent power supplies are employed, setting SW8-3 to OFF could contribute to the issue. To troubleshoot, initiate a power supply reset for both the indoor FTC and outdoor Ecodan, starting with the indoor unit followed by the outdoor unit. Examine the interconnecting cable for secure connections and proper voltages, and check the LEDs on the indoor FTC. If the problem persists, power down the entire system and set SW8-3 to ON before powering up the FTC followed by the Ecodan.