Freshdesk Solution Article - Technical Support Step-by-Step Phone Instructions
Safety position: This guide is for phone support coaching of licensed and competent service personnel. Confirm isolation, PPE, correct test equipment and safe access before any live testing. High voltage is present: 415V AC three phase and DC bus voltage can be approximately 560-600V DC. Do not instruct customers or unqualified persons to remove covers or perform electrical tests.
ScopeSafetyQuick mapError codesPhone triage flowRemote signalIndoor/outdoor communicationPower checksFan motorsThermistorsPressure sensorsEEVCompressorIPM protectionDiode bridgeNo cooling/heatingDefrostTicket evidence
1. Document scope
| Area | Details |
|---|---|
| Models covered | Indoor: ARTC72LATU / ARTC90LATU Outdoor: AOTA72LALT / AOTA90LALT |
| System type | R410A inverter ducted, 415V 50Hz three phase 4W outdoor supply, wired remote controller system. |
| Primary source material | ARTC72/90LATU Service Instruction, ARTC72/90LATU Service Manual, IPM Protection troubleshooting sheet, and Service Agent Training component testing material. |
| Purpose | Provide a phone-support workflow with clickable jump links so Technical Support can quickly move to a component test such as fan motor, thermistor, EEV, pressure sensor, compressor/IPM, or communication. |
2. Quick map
Use this section while speaking to the agent. The links jump directly to the test section.
| Symptom / error family | Most likely area | Jump to |
|---|---|---|
| E01 / E13 serial communication issues | Indoor/outdoor signal or wiring | Communication test |
| E00 wired remote controller error | Remote controller supply or Y1/Y2/Y3 signal | Remote signal test |
| E0A / E06 / E0C / E0E / E15 thermistor errors | Thermistor, wiring, connector, PCB return voltage | Thermistor testing |
| E16 pressure switch / pressure sensor error | Pressure transducer 5V supply, return voltage, diode check | Pressure sensor test |
| E17 IPM protection | Connection, airflow, outdoor fan, compressor, inverter PCB | IPM protection flow |
| E1b outdoor fan error | Outdoor DC fan motor, obstruction, feedback signal | Fan motor test |
| E19 inverter voltage protection | 415V AC input, DC bus, diode bridge, fuses, inverter board | Power checks / Diode bridge |
| E2F low pressure or no cooling/heating | Valves, refrigerant charge, EEV, strainer, airflow | No cooling/heating flow |
| Drain fault / water issue | Drain pump, float switch, drain restriction | Drain and float switch |
3. Error code quick reference
The wired remote controller and outdoor 7-segment display should be cross-checked. On the outdoor board, the ERROR lamp flashes rapidly; press ENTER to show the error content, then SELECT to scroll stored errors.
| Code | Fault | Priority test link |
|---|---|---|
| E01 | Serial error - reverse transfer | Serial communication |
| E13 | Serial error - forward transfer / indoor signal error | Serial communication |
| E00 | Wired remote controller error | Remote signal |
| E02 | Room temperature thermistor error | Thermistors |
| E04 | Indoor heat exchanger middle thermistor error | Thermistors |
| E06 | Outdoor heat exchanger outlet thermistor error | Thermistors |
| E0A | Outdoor temperature thermistor error | Thermistors |
| E0C | Outdoor discharge pipe thermistor error | Thermistors |
| E0E | Heat sink thermistor inverter error | Thermistors |
| E0F | Discharge temperature error | Refrigeration / airflow |
| E15 | Compressor thermistor error | Thermistors |
| E16 | Pressure switch / pressure sensor error | Pressure sensor |
| E17 | IPM protection | IPM protection |
| E1A | Compressor location detection error | Compressor |
| E1b | Outdoor fan error | Fan motor |
| E19 | Inverter voltage protection | Power / Diode bridge |
| E24 | Excessive high pressure protection on cooling | Airflow / heat exchanger |
| E2A | Power supply frequency detection error | Power checks |
| E2b | Compressor temperature error | Refrigeration / compressor temp |
| E2E | Inverter communication error | Power / Inverter PCB |
| E2F | Low pressure error | Low pressure flow |
| E34 / E37 | Indoor fan motor 1 or 2 lock / revolution error | Indoor fan motor |
| E38 / E39 | Indoor fan motor 1 or 2 driving circuit error | Indoor fan drive |
| E98 | Pump down error | Pump down |
| E99 | Indoor unit error condition | Check wired remote error and indoor PCB/communication |
4. Phone triage flow
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5. Remote signal test
Use this where the wired remote controller is blank, has E00, intermittent control, or no response.
1
Ask the agent to identify if the controller is wired as 2-wire or 3-wire. For 3-wire, test at Y1, Y2 and Y3.
2
Measure Y1 to Y3. Expected: 12V DC, no less than 11.4V DC. If missing, suspect controller board/supply path.
3
Remove Y2 and test between Y3 and the disconnected Y2 cable going to the indoor unit. Expected: fluctuating 7-11V DC pulse.
4
Test between Y3 and Y2 terminal. Expected: fluctuating 7-11V DC pulse.
Phone note: If Y1-Y3 supply is correct but the pulse is absent, determine whether the failure follows the controller, cable, or indoor PCB before quoting parts.
6. Indoor/outdoor serial communication test
Use for E01, E13, intermittent operation, or when either unit is not proving communication.
1
Confirm correct 415V outdoor supply and indoor supply path. Confirm terminals 1, 2, 3 are not crossed and that the signal cable is not loose, open, damaged, or connected to earth.
2
Communication is measured on DC volts between Neutral and Signal. Black lead to Neutral, red lead to Signal.
3
Isolate power, remove signal cable from Terminal 3 at the outdoor unit, re-apply power and test each direction separately.
4
For ARTC indoor signal, expected signal is generally 60-120V DC.
5
For AOTA outdoor signal, expected signal is generally 40-90V DC.
6
If one side is 0-5V DC while the other side produces signal, the side with 0-5V DC is the likely communication fault area. Reconfirm with wiring disconnected before condemning a board.
Do not skip: Reset power after correcting removed connectors or mis-wiring. Confirm no signal wire short to earth.
7. Power and DC bus checks
Use for no operation, E19 inverter voltage protection, inverter communication errors, no DC bus, no fan/compressor output, or repeated PCB failures.
1
Confirm outdoor supply: 415V AC phase-to-phase across L1-L2, L2-L3 and L1-L3. Confirm approximately 240V AC phase-to-neutral/earth.
2
Confirm fuses and hard-wired fuses are intact with power isolated. Do not bypass fuses.
3
Confirm the inverter DC output / DC bus. Three phase bridge rectifier output should be approximately 560-600V DC between + and -.
4
Confirm low-voltage PCB supplies where available: thermistors generally use 5V DC, EEV/fresh air/heater control can use 12V or 13V DC depending on connector, and fan control can use 15V DC.
5
If AC is present but DC bus is absent, test the bridge rectifier, inverter PCB, main relay path, fuses, fan motor, EEV coil, thermistors and pressure transducer before replacing PCB.
Jump to diode bridge test | Jump to IPM test | Jump to fan motor test
8. DC fan motor testing - indoor and outdoor
Use for E1b, E34, E37, E38, E39, non-starting fan, fan hunting, overheat/high pressure faults or IPM protection where airflow is suspect.
1
Confirm the fan blade/wheel rotates freely by hand with power isolated. Check bearings, foreign matter, wheel rub and water damage.
2
Do not disconnect or reconnect fan motor plugs with power applied. Isolate power and wait for DC bus discharge.
3
For standard DC brushless fan motors, use diode test, not resistance. Resistance can be misleading.
| Test | Expected value |
|---|---|
| Red lead RED, black lead BLACK | O/L |
| Red lead WHITE, black lead BLACK | 0.5V to 1.8V, depending on motor generation |
| Black lead BLACK, red lead RED | 0.8V to 1.1V |
| Black lead BLACK, red lead WHITE | 0.4V to 0.6V |
4
On live checks only by competent persons, confirm high-voltage fan supply and control supply at the plug. Typical training values are high voltage DC 330-380V DC, DC ground black, and 15V DC control power white on standard fan motor types.
5
If a fan motor fails diode test, is seized, or has damaged feedback/speed wiring, replace the fan motor before replacing the PCB. A failed fan can damage the board.
Critical: Never unplug the DC fan motor while powered. This can damage the PCB and create a safety risk.
9. Thermistor testing
Use for E02, E04, E06, E0A, E0C, E0E, E15 or any protection fault where sensor value drives control.
1
Power-on test: measure from DC ground to one side of the thermistor plug. Expected supply is generally 5V DC.
2
Measure return voltage from DC ground to the other thermistor wire. Return voltage should be below 5V DC and should align with bulb temperature.
3
Power-off test: unplug the thermistor and measure resistance in kΩ. Confirm bulb temperature and compare against thermistor table or Mobile Technician conversion tool.
4
Inspect physical condition: bulb seated in holder, cable not pinched, connector not corroded, no moisture damage, no short to earth.
| Training reference at 20°C | Resistance / return voltage guide |
|---|---|
| Room temperature | Approx. 12.53kΩ / 2.21V |
| Indoor heat exchanger temperature | Approx. 62.90kΩ / 2.21V |
| Discharge temperature | Approx. 64.50kΩ / 0.83V |
| Compressor temperature | Approx. 62.55kΩ / 0.86V |
| Outdoor temperature | Approx. 12.64kΩ / 3.75V |
| Outdoor heat exchanger / liquid / suction style sensors | Approx. 6.10kΩ family, verify exact thermistor table for this model |
Phone note: Do not condemn a PCB until the thermistor has been unplugged and checked against temperature. A thermistor short to earth can damage the main/controller PCB.
10. Pressure switch and pressure transducer testing
Use for E16 pressure switch/sensor error, E24 high pressure, E2F low pressure, discharge temperature issues, or abnormal pressure readings.
1
Power-on: pressure transducers use a 5V DC supply. Red to black should be 5V DC.
2
Return voltage is measured black to white. For discharge pressure, the return voltage is approximately equal to pressure in kPa x 1000 relationship used in training; for example 2.5V DC approx. 2500kPa.
3
Power-off and unplugged: use diode test. Confirm no wire is shorted to earth.
| Diode test | Expected |
|---|---|
| Black lead BLACK, red lead WHITE | 1.0V to 1.1V |
| Black lead BLACK, red lead RED | 1.2V to 1.3V |
| Black lead WHITE, red lead RED | 1.6V to 1.7V |
| Black lead WHITE, red lead BLACK | 0.6V to 0.7V |
| Black lead RED, red lead BLACK | 0.5V to 0.6V |
| Black lead RED, red lead WHITE | 0.6V to 0.7V |
| Earth to red/white/black | O/L |
4
If pressure reading is not plausible, compare with gauges, refrigerant state, operating mode, valve position and known pressure limits before replacing sensor.
11. Electronic expansion valve (EEV) testing
Use for low pressure, high discharge temperature, poor performance, compressor temperature, EEV noise or suspected metering fault.
1
On power-up, listen/feel for EEV initialisation. The ARTC/AOTA service instruction states EEV initialisation drives 528 pulses toward closing under start-up/interval conditions.
2
Confirm EEV pulse range for these models: 50-480 pulses in cooling/dry and 40-480 pulses in heating. When compressor is stopped, the EEV is set at 480 pulses.
3
Power-off resistance test. Match the actual connector type. Always test each winding to earth for O/L and inspect corrosion under the coil.
| EEV type | Resistance check |
|---|---|
| 5-wire 12V coil | Red to white/orange/yellow/blue = 45-50Ω. Each wire to earth = O/L. |
| 6-wire 12V coil | Red to white/orange = 45-50Ω. Brown to yellow/blue = 45-50Ω. Each wire to earth = O/L. |
4
If resistance is correct, check whether the coil is clipped firmly to the body and whether the valve body/strainer is restricted. Temperature difference across a strainer can indicate blockage.
12. Compressor testing
Use for E1A compressor location detection, IPM protection, no start, abnormal noise, trip, or stops soon after starting.
1
Power isolated: confirm compressor harness is tight, correctly connected and not open circuit.
2
Measure winding resistance between U-V, V-W and U-W. All three windings should be equal, normally approximately 1-2Ω around 20-25°C.
3
Insulation test from each winding to earth. Expected: greater than 1MΩ.
4
If resistance/insulation is normal but compressor stops soon after starting, confirm gas and liquid valves open, no refrigerant leak/undercharge, no strainer restriction and no oil/refrigerant circuit blockage before replacing compressor.
5
If the compressor is mechanically noisy, locked, or readings are abnormal, escalate for compressor replacement assessment and capture all readings/photos.
13. IPM protection flow - E17
Use this section for E17 / IPM Protection. The IPM protection sheet identifies the detective actuators as the outdoor inverter PCB and compressor. It also flags connection failure, outdoor fan operation failure, outdoor heat exchanger clogging, compressor failure and inverter PCB failure.
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Detection behaviour: when over-current flows in the inverter PCB, the compressor stops. If the same error repeats within 40 seconds after restart and repeats 5 times, the compressor stops permanently.
Important: Do not move straight to inverter PCB. Confirm airflow and fan motor first. A failed fan or blocked coil can drive the IPM protection fault.
14. IPM and diode bridge power-off tests
Use diode mode with power isolated and DC bus discharged. Disconnect control harnesses where required before testing PCB/inverter components.
IPM / TR PCB diode guide
| Test | Expected |
|---|---|
| Black lead P, red lead U/V/W | Approx. 0.4V each |
| Black lead U/V/W, red lead N | Approx. 0.4V each |
| Black lead P, red lead N | 0.7V to 0.9V |
| Black lead N, red lead P | O/L |
Three phase bridge rectifier guide
| Test | Expected |
|---|---|
| Power on AC input | L1-L2, L2-L3, L1-L3 = 415V AC |
| Power on phase to earth/neutral | Approx. 240V AC |
| Power on DC output + to - | Approx. 560-600V DC |
| Power off diode: black lead +, red lead AC1/AC2/AC3 | Approx. 0.4V each |
| Power off diode: black lead AC1/AC2/AC3, red lead - | Approx. 0.4V each |
| Power off diode: black lead +, red lead - | 0.7V to 0.9V |
| Power off diode: black lead -, red lead + | O/L |
Safety: DC bus can remain charged after isolation. Confirm discharge before touching or unplugging inverter components.
15. No cooling / no heating / pressure protection flow
Use for poor performance, E0F discharge temperature, E2b compressor temperature, E24 high pressure, E2F low pressure or repeat protection stops.
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Low pressure focus - E2F
Check valves open, outdoor ambient within range, outdoor fan and heat exchanger, EEV/strainer condition, low pressure sensor characteristics, solenoid valve operation and refrigerant quantity.
High pressure focus - E24
Check outdoor airflow, outdoor coil fouling, fan speed, installation clearances, short cycling/recirculation, overcharge, non-condensables and pressure sensor accuracy.
16. Defrost and heating-specific checks
Use where heating performance is questioned, outdoor fan stops in heating, defrost icon appears, or frosting is reported.
1
Confirm whether the unit is in normal defrost. Outdoor fan OFF and compressor control changes can be normal during defrost.
2
Defrost release is based on outdoor heat exchanger temperature over 10°C or compressor ON time over approximately 15-20 minutes.
3
During defrost flow in the service instruction, EEV and compressor speed are actively controlled. For AOTA72LALT, compressor defrost speed can be 70-95 rps; AOTA90LALT can be 100 rps. EEV values differ by model.
4
If defrost is excessive or incomplete, check outdoor thermistor seating/value, outdoor coil airflow, refrigerant charge, valve position and ambient/site conditions.
17. Drain pump and float switch
Use for water leak, drain fault, float switch activation, or indoor unit stops with drain-related symptoms.
1
Confirm drain pan, pump, hose, trap and fall are clear. Check safety drain path where fitted.
2
Confirm float switch wiring/connector is seated and not bridged incorrectly.
3
Confirm pump supply and operation. If pump runs but water remains, check blockage or incorrect drain installation.
4
Record whether the fault clears after drain pan is emptied and float returns to normal state.
18. Pump down reminder
Use only where pump down is authorised and safe. Follow the service instruction sequence exactly.
1
Confirm liquid and gas stop valves are fully open before beginning.
2
Hold PUMP DOWN button SW102 for over 3 seconds. Compressor and outdoor fan start automatically.
3
When display shows run, close liquid valve immediately.
4
When display changes to the next close prompt, close gas valve immediately.
5
When End displays, compressor and outdoor fan stop automatically after approximately 1 minute, then turn power off.
Error: If E98 pump down error appears, recover refrigerant from the service port rather than continuing pump down attempts.
19. Ticket evidence checklist
| Required evidence | Detail to request |
|---|---|
| Model and serial | Indoor and outdoor model/serial photos. Confirm ARTC72/90 with AOTA72/90. |
| Exact error evidence | Photo of wired remote error and outdoor 7-segment error. Include stored errors if multiple. |
| Power readings | L1-L2, L2-L3, L1-L3, phase-to-neutral/earth, DC bus + to -, fuse continuity. |
| Communication readings | Indoor signal value, outdoor signal value, test condition with signal wire disconnected. |
| Component test photos | Meter readings for fan diode test, thermistors, pressure sensor, EEV coil, compressor resistance/insulation, IPM/bridge diode test. |
| Site and airflow | Photos of outdoor coil, clearances, obstructions, duct/filter/return air condition, indoor coil if accessible. |
| Refrigeration evidence | Valve position, pressure readings, leak evidence, strainer temperature difference, recharge/vacuum details if performed. |
| Decision | State whether fault is wiring/site/refrigeration/component/PCB and what part is authorised. |
Internal note: This article is designed for Freshdesk source view. Internal links are anchor links, so agents can jump directly to tests while on the phone.