Air conditioners produced by the Tokyo-based company Hitachi require frequent servicing. If this requirement is neglected, the system becomes especially prone to failures. However, they can take place even in case your air conditioner is serviced in time. The table below provides you with advice on what to do in case something goes wrong.
| Code No. | Category | Type of Abnormality | Main cause |
| 1 | Indoor unit | Activation of protection device (float switch) | Failure of fan motor, drain discharge, PCB, relay, float switch activated. |
| 2 | Outdoor unit | Activation of protection device (high pressure cut) | Activation of PSH, locked motor, abnormal operation in the power supply phase. |
| 3 | Transmission | Abnormality between indoor (or outdoor) and outdoor (or indoor) units | Incorrect wiring. Loose terminals, Failure of PCB. Tripping of fuse. Power supply OFF. |
| 4 | Abnormal operation between inverter and control PCB | Transmission failure between inverter PCBs | |
| 5 | Power supply | Abnormal power supply | Power source with abnormal wave pattern. |
| 6 | Voltage drop | Voltage drop due to excessively low or high voltage in outdoor unit | Voltage drop in power supply. Incorrect wiring or insufficient capacity of power supply wiring. |
| 7 | Drop in discharge gas overheating | Excessive refrigerant charge. Expansion valve lock open. | |
| 8 | Cyde | Increase in discharge gas temperature | Insufficient refrigerant charge, refrigerant leakage. Expansion valve closed or clogged. |
| 11 | Inlet air thermistor | ||
| 12 | Sensor in indoor unit | Outlet air thermistor Anti-freeze thermistor | Failure of thermistor, sensor, connection. |
| 14 | Gas pipe thermistor | ||
| 19 | Protection device for fan motor is triggered | Failure of fan motor | |
| 20 | Compressor thermistor | ||
| 21 | Outdoor unit sensor | Abnormality of high pressure sensor Outside air thermistor | Failure of thermistor, sensor, connection. |
| 24 | Evaporation thermistor | ||
| 31 | Incorrect setting of outdoor and indoor units | Incorrect setting of capacity code. | |
| 35 | System | Incorrect setting of indoor unit number | Duplication of indoor unit number. |
| 38 | Abnormality of protective circuit in outdoor unit | Failure of indoor unit PCB; incorrect wiring; connection to indoor unit PCB. | |
| 41 | Cooling overload (possible activation of high pressure device) | O.U. pipe thermistor temp, is higher than 55 °C and the compressor top temp, is higher than 95 °C, O.U. protection device is activated. | |
| 42 | Heating overload (high-pressure device may be activated) | If I.U. freeze protection thermistor temp, is higher than 55 °C and compressor top temp, is higher than 95 °C, O.U. protec- tion device is activated. | |
| 45 | Activation of high pressure increase protection device | If the discharge pressure (Pd) of the compressor is higher than 3.8MPa for 1 minute. | |
| 47 | Activation of protection device for low pressure drop | Stop due to excessive decrease of evaporating temper- ature (Temp < -35 °C) is activated 3 times in one hour, motor locked in heating mode. | |
| 48 | Activation of overcurrent protection | Overload, overcurrent. Failure of DIP IPM, IPM or PCB2, heat exchanger clogged, locked compressor. | |
| 51 | Abnormality in inverter current sensor | Incorrect wiring of current sensor. Failure of control PCB, DIP IPM, IPM or PCB2. | |
| 53 | Activation of transistor module protection device | Abnormality of DIP IPM or PCB2 Compressor failure, heat exchanger clogged. Abnormal inverter fin thermistor | |
| 54 | Abnormality of inverter fin temperature | Heat exchanger clogged. Abnormal outdoor fan. | |
| 55 | Abnormality of inverter module | Failure of DIP-IPM, IPM or PCB2. | |
| 57 | Fan motor abnormality | Disconnected wire or incorrect wiring between control PCB and inverter PCB. | |
| Incorrect wiring or abnormality in fan motor. | |||
| EE | Compressor protection alarm | Compressor failure. | |
| bO | Incorrect Setting of Unit Model | No Setting of Unit Model, Incorrect Setting of Unit Model | |
| b1 | Incorrect unit No. setting | Over 64 indoor units, setting by no. or indoor unit address. | |
| b5 | Incorrect Setting of Indoor Unit No. for H-LINK Type | An indoor unit not supporting H-LINK II is set the indoor unit No. as 16 and after. |