Freshdesk Solution Article - Technical Support Step-by-Step Phone Instructions
Safety position: This guide is for technical support coaching of licensed and competent service personnel only. Before live testing, confirm the technician has appropriate PPE, suitable test equipment, and authority to work on 415 V three phase equipment. For power-off tests, isolate supply and wait for capacitors to discharge before touching electrical components. Do not instruct consumers or unqualified persons to remove covers or perform electrical tests.
Quick mapSafetyModel scopeError triageCommunicationRemote signalPower / PFC / DC busIPM / inverterCompressorFan motorsThermistorsPressure sensorEEV4-way valveDrain / floatRefrigeration checksTest run / pump downTicket evidence
1. Document scope and source matching
This article matches the ARTC36/45/54/60LCTU indoor ducted units with AOTD36/45/54/60LATT and AOTD54LBTT outdoor units, using the service instruction and service manual information, then adding component testing methods from the Service Agent Training document.
| Area | Details for phone support |
|---|---|
| Models covered | ARTC36LCTU, ARTC45LCTU, ARTC54LCTU, ARTC60LCTU. Outdoor references include AOTD36LATT, AOTD45LATT, AOTD54LATT, AOTD60LATT and AOTD54LBTT. |
| System type | R410A, 415 V 50 Hz three phase 4 wire ducted inverter system. |
| Refrigerant and pipework | Service manuals list precharge 3,450 g, additional charge 50 g/m, max pipe length 75 m and max pipe height 30 m. Pipe sizes are 9.52 mm liquid and 15.88 mm gas. |
| Outdoor board family | Older 3 phase platform using main/controller PCB, inverter PCB, PFC PCB, capacitor PCB, power supply PCB, reactors, pressure sensor, EEV, 4-way valve and twin outdoor fan motors. Use the circuit diagram for connector location. |
| Agent training overlay | Use the training values for testing thermistors, pressure transducer, DC fan motors, EEV coils, diode bridge, IPM, compressor and 3 phase bridge rectifier. Where the training shows R32 board layouts, apply the test method to the equivalent ARTC/AOTD component and connector shown in the service manual. |
2. Safety and call control script
Opening script
Confirm you are speaking with a licensed technician. Confirm model, serial, power supply, error code, site conditions, and whether the fault is current or historical. Ask the technician not to disconnect DC fan motors, compressor plugs or PCB harnesses while power is applied.
- Live voltage checks: Only for qualified technicians. Confirm meter is set correctly before asking for AC or DC measurements.
- Power-off checks: Isolate all supplies. Wait for capacitors to discharge. Confirm DC bus voltage has dropped before unplugging boards or motors.
- Do not jump ahead: Always confirm power supply, connectors, airflow and fault history before condemning PCB, compressor or fan motors.
- Record evidence: Capture error display, voltages, resistance/diode readings, photos of connectors, coil condition, outdoor heat exchanger and pipe temperatures.
3. Error triage quick map
Use the wired remote controller and/or outdoor LED display first. Then follow the error pathway below. The outdoor main PCB error LED uses flash counts, while the wired remote controller displays an error code. Confirm the exact code before proceeding.
| Fault group | Typical manual error wording | Initial support direction |
|---|---|---|
| Serial / communication | Serial reverse transfer error, serial forward transfer error | Check terminals, 415 V supply to outdoor, 240 V indoor feed as applicable, neutral-signal serial line, noise/earth issues, then perform the communication test. |
| Indoor sensor / drain | Room thermistor, indoor heat exchanger thermistor, water drain error | Check connectors, sensor resistance, 5 V supply, float switch, drain hose and pump operation. |
| Outdoor thermistors | Discharge, outdoor, heat exchanger out/middle, compressor, heatsink INV/PFC | Check connector, physical bulb location, cable damage, 5 V supply and resistance against temperature. |
| Pressure / refrigeration | Pressure SW/sensor, low pressure, excessive high pressure, discharge temperature, compressor temperature | Check valves, charge/leak condition, outdoor coil airflow, EEV, strainers, pressure sensor output and thermistor placement. |
| Inverter / compressor | Over current, compressor start-up, compressor location detection, INV error, PFC PCB error | Check supply phase balance, connectors, fan operation, compressor windings/megger, diode bridge, IPM, PFC/inverter boards and heatpaste/heatsink condition. |
| Fan motor | Outdoor unit fan error, indoor fan motor lock/revolution error | Check motor shaft movement, connectors, DC supply, diode test values and board outputs. |
1. Confirm displayed error
Ask for the wired controller code and outdoor LED blink count. Confirm whether the code returns immediately or only after compressor starts.
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2. Check power and connectors
Loose terminals, removed connectors, mis-wiring, open cable and incorrect phase/neutral must be corrected before component diagnosis.
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3. Match the fault group
Sensor faults go to thermistor or pressure checks. Inverter faults go to IPM/diode/compressor/fan checks. Communication faults go to serial signal test.
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4. Complete one full test path
Do not replace a board until connectors, load components and site conditions have been eliminated.
4. Communication fault - indoor/outdoor serial test
For this older ARTC/AOTD platform the service instruction references AC serial signal checks around terminal 2-3, while the agent training explains the broader method of separating indoor and outdoor signal responsibility. Use the service manual terminal numbering and the actual wiring diagram on site.
| Check | Expected / action |
|---|---|
| Terminal and supply check | Confirm correct power supply at outdoor: 415 V three phase between phases and approximately 240 V phase to neutral. Confirm terminal 1-2 / L-N supply according to the model wiring. |
| Connection check | Check loose terminal screws, removed connectors, open cable, mis-wiring, water ingress, corrosion and poor earth. Reset power after correcting wiring. |
| Serial signal check | Service instruction serial checks reference a swinging value around AC70 V to AC130 V at outdoor terminal 2-3 for older serial transfer checks. If abnormal after wiring/power checks, suspect the board responsible for that direction of transfer. |
| Agent training method | Isolate, separate the signal line where required, then identify whether the indoor or outdoor side is producing the communication signal. For model families using DC serial, the training summary lists AOTD around 40-90 V and ARTG/3 phase around approx. 295 V static; however this ARTC/AOTD manual specifically references the AC serial terminal check. |
Phone wording
Ask the technician to tell you whether the error is forward transfer or reverse transfer. Then direct them to check the interconnecting cable and terminal condition before any board diagnosis. If the serial voltage test is abnormal with wiring proven, escalate to controller/main PCB diagnosis based on the direction of the error.
5. Wired remote controller signal test
Where the wired remote is used, verify controller supply and signal before replacing indoor PCB or controller.
| Test | Expected result |
|---|---|
| Y1 to Y3 / power feed | 12 V DC. Agent training states no less than 11.4 V DC. If missing, check indoor controller board power supply to remote. |
| Y2 signal test | Disconnect Y2 at the remote and test between Y3 and the wire to indoor. Expect a fluctuating 7-11/12 V DC pulse according to training method. |
| Y2 to Y3 terminal | Expect fluctuating 7-11/12 V DC pulse. If there is no signal, check wiring and controller. |
| Manual-specific note | The SI wired remote controller troubleshooting states to check terminal connection/disconnection and then check DC12 V at the relevant indoor controller PCB connector; if DC12 V is present at the PCB, suspect the wired remote controller; if DC0 V, suspect controller PCB. |
6. Power, PFC and DC bus checks
These units are 415 V 3 phase 4 wire. Establish the power foundation before testing inverter components.
| Test point | Expected / action |
|---|---|
| Incoming supply | Phase-to-phase L1-L2, L2-L3, L1-L3 should be around 415 V AC. Each phase to neutral/earth is around 240 V AC. |
| Three phase bridge rectifier power on | Agent training states DC OUT + to - should be 560-600 V DC on 3 phase bridge rectifier power-on checks. |
| Fuses and reactors | Check hard-wired fuses for continuity with power off. Check reactors for physical damage, overheating or open circuit if PFC/inverter errors are present. |
| PFC PCB error path | Check connection between main PCB and PFC PCB. Service instruction notes PFC communication/circuit error and output voltage over DC760 V as detection conditions. Check DC15 V supply at the specified main PCB connector before condemning PFC PCB. |
| Momentary power / over voltage | If present, check supply stability, phase loss, loose neutral, supply quality and recent power events. |
Do not skip
If a circuit breaker trips immediately, isolate load components before condemning PCB. Check compressor, fan motors, diode bridge, IPM/PFC and wiring for short circuits.
7. IPM, inverter and diode bridge checks
Use power-off diode testing from the agent training and apply it to the ARTC/AOTD inverter PCB / PFC layout shown in the service manual. Disconnect control harnesses during power-off tests.
| Component | Power-off test values from agent training |
|---|---|
| IPM / TR PCB | P to U/V/W approx. 0.4 V. U/V/W to N approx. 0.4 V. P to N approx. 0.7-0.9 V. N to P should be O/L. |
| 1 phase diode bridge where fitted | + to AC legs approx. 0.4 V, AC legs to - approx. 0.4 V, + to - approx. 0.7-0.9 V, - to + O/L. |
| 3 phase diode bridge | + to AC1/AC2/AC3 approx. 0.4 V. AC1/AC2/AC3 to - approx. 0.4 V. + to - approx. 0.7-0.9 V. - to + O/L. |
| Heatsink / heatpaste | When replacing inverter, PFC, IPM or diode bridge parts on a heatsink, remove old heatpaste completely and apply an even new layer. Do not use an impact driver on fine thread screws. |
| Board replacement rule | Do not replace inverter/PFC PCB until fan motor, compressor, supply, connectors, airflow, heat exchanger condition and diode checks are completed. |
1. Inverter fault displayed
Confirm exact code: over current, compressor start-up, compressor location, INV, PFC or fan error.
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2. Inspect load components
Check fan motor shaft, compressor windings, connectors and outdoor coil airflow.
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3. Power-off diode tests
Test diode bridge and IPM using diode mode. Disconnect harnesses first.
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4. Decision
If load components and wiring are normal and diode values fail, replace affected inverter/PFC board. If values pass but fault remains, escalate with recorded readings.
8. Compressor checks
| Check | Expected / instruction |
|---|---|
| Winding resistance | Agent training: all 3 windings should be equal, typically around 1-2 ohm at 20-25°C. Measure U-V, V-W and U-W with power isolated. |
| Insulation resistance | Greater than 1 megaohm from any winding to earth. Use correct megger procedure for inverter compressor and disconnect from PCB before testing. |
| Mechanical/refrigerant checks | If compressor temperature, discharge temperature, over current or start-up errors occur, also check valves open, correct charge, restrictions, EEV, strainers, airflow, coil clogging and outdoor fan operation. |
| Service instruction overlay | For over current or compressor start-up faults, the SI path checks connections, outdoor fan, outdoor heat exchanger, compressor, then inverter PCB. |
Phone decision point
If windings are unequal, shorted or low to earth, stop electrical reset attempts and escalate compressor replacement. If windings pass, continue inverter/IPM and refrigeration-side checks.
9. Indoor and outdoor fan motor checks
The ARTC/AOTD service manuals identify indoor and outdoor fan motors and show upper/lower outdoor fan motors on the circuit diagram. Use the exact connector location from the service manual, then apply the agent training test method.
| Fan check | Expected / instruction |
|---|---|
| Mechanical check | With power isolated, check the fan blade/shaft is not seized, rubbing or obstructed. Check outdoor coil is not blocked. |
| Do not unplug live | Agent training is explicit: do not disconnect DC brushless fan motors when power is applied. |
| DC fan motor diode test | Red lead to red, black lead to black = O/L. White to black = 0.5-1.8 V. Black to red = 0.8-1.1 V. Black to white = 0.4-0.6 V. Results vary by motor generation. |
| Supply principle | Many DC fan motors operate on high voltage DC 330-380 V and 15 V DC control circuit. This platform also includes fan reactors/capacitor circuits; verify against the actual circuit diagram before applying the generic R32 board voltage labels. |
| Error path | For outdoor fan errors, check connections first, then fan motor, then output/drive board. Do not replace main/inverter PCB until fan motor testing is recorded. |
10. Thermistor checks
| Power state | Method |
|---|---|
| Power on | Measure 5 V DC supply from DC ground to one side of the thermistor. Return voltage on the other side should be below 5 V and must correspond to temperature. |
| Power off | Unplug thermistor and measure resistance in k ohms. Compare to the relevant service manual thermistor graph/table for that sensor type. |
| Physical inspection | Check bulb is clipped/located correctly, cable is not pinched, damaged, wet or shorted to earth. A thermistor short to earth may damage the controller PCB. |
| Room thermistor guide | Service instruction room thermistor examples include approx. 12.5 kΩ around 20°C and approx. 10.0 kΩ around 25°C. Use the manual chart for final judgement. |
| Heat exchanger/discharge/compressor thermistors | These have different curves. Do not compare discharge or compressor thermistors to room thermistor values. |
Common phone trap
A sensor can be electrically correct but physically misplaced. Always ask whether the thermistor is on the correct holder and properly touching the pipe or coil.
11. Pressure sensor / pressure switch checks
| Test | Expected / instruction |
|---|---|
| Power on supply | Pressure transducer uses 5 V DC. Training method: red to black = 5 V DC supply. Black to white = return voltage. |
| Return voltage guide | Training note: discharge pressure voltage is approximately equal to discharge pressure; for example 2.5 V DC return is approximately 2500 kPa. The earlier sensor example also notes 1.14 V = 800 kPa. |
| Power off diode test | Black lead to white = 1.0-1.1 V, black to red = 1.2-1.3 V, white to red = 1.6-1.7 V, white to black = 0.6-0.7 V, red to black = 0.5-0.6 V, red to white = 0.6-0.7 V. Earth to red/white/black = O/L. |
| Service instruction pressure sensor error | Check pressure sensor connection, 5 V supply at PCB side connector, then pressure sensor output. If supply is incorrect, suspect main PCB; if supply is correct but output is wrong, suspect pressure sensor. |
| Low pressure error | Also check gas leak/undercharge, valves open, EEV/strainer restriction and pressure sensor output. |
12. Electronic expansion valve checks
The service instruction states EEV pulse control and initialization logic, while the agent training provides coil resistance methods. Confirm whether the installed coil is 5-wire or 6-wire before testing.
| EEV type | Power-off expected resistance |
|---|---|
| 5 wire EEV coil | Red to white/orange/yellow/blue = 45-50 ohm. Each conductor to earth = O/L. |
| 6 wire EEV coil | Red to white/orange = 45-50 ohm. Brown to yellow/blue = 45-50 ohm. Each conductor to earth = O/L. |
| Physical check | Check corrosion underneath coil, coil fully clipped down, valve body not damaged and wiring not pinched. |
| Manual operating logic | The EEV is driven by a DC step motor. Standard pulse range is typically 0-480 pulses; the service instruction for these models uses EEV control as part of discharge temperature and operating condition management. |
13. 4-way valve / reversing valve checks
| Check | Expected / instruction |
|---|---|
| Operating logic | Training notes Fujitsu outdoor units commonly use AC 240 V to the reversing/4-way valve solenoid throughout heating on AC solenoid models. |
| Manual logic | Service instruction notes 4-way valve extension when switching from cooling to heating: compressor stops, then valve switches after a delay. |
| Electrical check | Confirm valve coil connector and output according to circuit diagram. Check coil resistance and supply only when qualified and safe. |
| Refrigeration check | If valve is energised but performance is wrong, compare pipe temperatures and operating pressures. Consider stuck valve, low charge or EEV/restriction faults. |
14. Drain pump and float switch checks
| Check | Expected / instruction |
|---|---|
| Float switch | Check float switch status and connector. The SI water drain error path checks float switch, CN9/wiring and drain hose. |
| Drain hose | Check blockage, fall, trapped water, site installation and pump discharge. |
| Power/control | Confirm pump operation and controller output only with qualified technician. Check for water in drain pan and evidence of intermittent float activation. |
| Ticket evidence | Request photos of drain pan, pump, drain route, float connector and any site trap/termination. |
15. Refrigeration and airflow checks
Many inverter faults are caused by site or refrigeration conditions. Use these checks before condemning electrical boards.
| Symptom/error | Ask technician to check |
|---|---|
| High pressure / discharge temperature | Outdoor coil blocked, outdoor fan failure, fan airflow recirculation, valves open, overcharge, EEV/strainer restriction, thermistor placement and ambient conditions. |
| Low pressure | Low charge/leak, valves open, EEV stuck/restricted, indoor airflow problem, blocked filters, blocked coil, pressure sensor output. |
| Compressor temperature | Gas valve open, correct charge, outdoor fan/coil, EEV/strainer, compressor thermistor installed correctly. |
| Poor performance no code | Static pressure, filters, duct restriction, return air, spill/constant zones, correct model capacity, pipe length/charge and installation clearances. |
16. Test operation and pump down
| Function | Support instruction |
|---|---|
| Test operation | Use the procedure in the service instruction for test operation. Confirm mode, allow sufficient start-up time, and monitor for repeat fault within the first few minutes. |
| 3-minute restart prevention | Do not assume no-start is a fault immediately after a stop. The system prevents compressor restart for approximately 3 minutes. |
| Pump down | Use only for qualified technicians following the service instruction. Confirm valves are open before starting, then close the liquid valve at the correct display stage and gas valve at the correct stage. If pump down fails, recover refrigerant from service port. |
| Forced cooling | Use only when required and only as per the service instruction. Record whether compressor, outdoor fan and indoor fan start normally. |
17. Ticket evidence checklist
- Model and serial numbers for indoor and outdoor units.
- Exact error code from wired remote and outdoor LED blink count or display.
- Photo of outdoor and indoor wiring terminals before changes.
- Supply readings: phase-to-phase, phase-to-neutral, terminal 1-2/2-3 serial where applicable, and any DC bus readings.
- Component readings: compressor U/V/W resistance and megger, fan motor diode test, pressure sensor 5 V supply and return, thermistor resistance/return voltage, EEV coil resistance.
- Site checks: outdoor coil condition, fan operation, filters, airflow, duct/static pressure concerns, pipe length/charge, valve positions and evidence of leaks.
- Decision taken: reset, wiring correction, further test requested, part replaced, or escalation.
Escalation wording
Escalate when the technician has provided readings that conflict with the expected values, when multiple components appear abnormal, when there is repeated board failure, or when site conditions may be causing recurring protection errors.
Source material matched: ARTC54LCTU service instruction, ARTC54LCTU service manual, ARTC36/45/60LCTU and AOTD36/45/60LATT service manual, AOTD60LATT service manual, and Service Agent Training component testing document. This article is designed for Freshdesk source view with inline formatting.