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ARTC72LATU / ARTC90LATU and AOTA72LALT / AOTA90LALT
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. For power-off inverter tests, isolate and wait for capacitors to discharge before touching components.
ScopeQuick mapError codesPhone triageRemote signalSerial commsPower / DC busFan motorsThermistorsPressure sensorsEEVCompressorIPMDiode bridgeDischarge tempLow pressureHigh pressurePump downTicket evidence
1. Document scope
| Area | Details |
|---|---|
| Models covered | Indoor: ARTC72LATU / ARTC90LATU Outdoor: AOTA72LALT / AOTA90LALT |
| System type | R410A inverter ducted system, 415V 50Hz three phase 4-wire outdoor supply, wired remote controller system. |
| Primary source material | ARTC72/90LATU Service Instruction and Service Agent Training component testing material. The layout and navigation has been rebuilt to match the supplied GREAT HTML style. |
| Purpose | Give Technical Support a consistent phone workflow with clickable jump links, flowcharts, expected readings, component tests and ticket evidence requirements. |
How to use this guide on a call: confirm model and exact error, complete the safety gate, check the basics, then follow the linked flowchart. Record readings before recommending parts.
2. Quick map
Use this section while speaking to the service agent. Each item links to the relevant component test or flowchart.
| Symptom / error family | Most likely area | Jump to |
|---|---|---|
| Unit has no exact error yet | Use intake questions and outdoor display error history. | Phone triage flow |
| Remote controller issue / E00 | Wired controller power or Y1/Y2/Y3 communication. | Remote signal test |
| E01 / E13 communication | Indoor/outdoor power and serial signal split. | Serial communication flow |
| E02 / E04 / E06 / E0A / E0C / E0E / E15 | Thermistor connector, resistance and 5V supply. | Thermistor testing |
| E16 / pressure related | Pressure sensor 5V supply, return voltage and pressure switch. | Pressure sensor test |
| E17 / E19 / E2E | Inverter board, IPM, diode bridge, DC bus, compressor. | IPM / Diode bridge |
| E1b / indoor fan errors | DC fan motor obstruction, diode test and board output. | Fan motor testing |
| E0F / E2b / E2F / E24 | Refrigeration, airflow, valves, EEV, charge, pressure. | Discharge temp / Low pressure |
3. Error code quick reference
Outdoor display: when an error occurs, the outdoor ERROR lamp flashes rapidly. Press ENTER to show the error content, then use SELECT to scroll stored errors. Cross-check with the wired remote display before diagnosing.
| Code | Fault / description | Phone support action |
|---|---|---|
| E01 | Serial reverse transfer error | Outdoor unit cannot properly communicate back to indoor. Jump to test / flow |
| E13 | Serial forward transfer / indoor signal error | Indoor unit cannot properly receive serial signal from outdoor. Jump to test / flow |
| E00 | Wired remote controller error | Check Y1/Y2/Y3 remote controller communication. Jump to test / flow |
| E02 | Room temperature thermistor error | Connector, thermistor resistance, 5V PCB supply. Jump to test / flow |
| E04 | Indoor heat exchanger middle thermistor error | Connector, thermistor resistance, 5V PCB supply. Jump to test / flow |
| E06 | Outdoor heat exchanger outlet thermistor error | Connector, thermistor resistance, 5V PCB supply. Jump to test / flow |
| E0A | Outdoor temperature thermistor error | Connector, thermistor resistance, 5V PCB supply. Jump to test / flow |
| E0C | Outdoor discharge pipe thermistor error | Connector, thermistor resistance, 5V PCB supply. Jump to test / flow |
| E0E | Heat sink thermistor inverter error | Connector, heatsink thermistor, inverter PCB 5V supply. Jump to test / flow |
| E0F | Discharge temperature error | Refrigerant charge/leak, valves, EEV/strainer, airflow, thermistor. Jump to test / flow |
| E15 | Compressor thermistor error | Connector, compressor thermistor, Main PCB 5V supply. Jump to test / flow |
| E16 | Pressure switch / pressure sensor error | 5V supply, return voltage, pressure switch continuity. Jump to test / flow |
| E17 | IPM protection | Connection, airflow, outdoor fan, compressor, inverter PCB/IPM. Jump to test / flow |
| E18 | Outdoor CT error | Check outdoor current detection circuit and wiring. Jump to test / flow |
| E1A | Compressor location detection error | Compressor winding and inverter output checks. Jump to test / flow |
| E1b | Outdoor fan error | Outdoor DC fan obstruction, plug, diode test, feedback. Jump to test / flow |
| E19 | Inverter voltage protection | 3 phase AC input, DC bus, diode bridge, inverter board. Jump to test / flow |
| E24 | Excessive high pressure protection on cooling | Outdoor airflow, condenser restriction, fan, overcharge, pressure sensor. Jump to test / flow |
| E2A | Power supply frequency detection error | Supply voltage, phase/neutral, harmonic/noise, grounding. Jump to test / flow |
| E2b | Compressor temperature error | Valves, EEV/strainer, gas charge, compressor thermistor, fan, coil restriction. Jump to test / flow |
| E2E | Inverter communication error | Main PCB to inverter PCB low voltage and communication. Jump to test / flow |
| E2F | Low pressure error | Low charge/leak, pressure sensor, EEV/strainer, valves, airflow. Jump to test / flow |
| E34 / E37 | Indoor fan motor lock / revolution error | Indoor fan obstruction, motor plug, diode/resistance check, PCB. Jump to test / flow |
| E38 / E39 | Indoor fan motor driving circuit error | Indoor fan motor, filter/power PCB, controller PCB. Jump to test / flow |
| E98 | Pump down error | Follow pump down recovery process and recover refrigerant if needed. Jump to test / flow |
| E99 | Indoor unit error shown at outdoor display | Check indoor error display and indoor PCB / communication. Jump to test / flow |
4. Phone triage flow
Phone triage flow
1. Confirm caller competency and safety.
Licensed/competent technician onsite, correct PPE and meter, safe access, no live work by customers.
Licensed/competent technician onsite, correct PPE and meter, safe access, no live work by customers.
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2. Capture the basics.
Model numbers, serial numbers, installation age, refrigerant pipe length, symptoms, exact wired remote error and outdoor 7-segment error.
Model numbers, serial numbers, installation age, refrigerant pipe length, symptoms, exact wired remote error and outdoor 7-segment error.
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3. Confirm installation conditions.
Valves open, filters/coils clear, ductwork/airflow reasonable, no blocked outdoor discharge, no signs of water ingress or vermin damage.
Valves open, filters/coils clear, ductwork/airflow reasonable, no blocked outdoor discharge, no signs of water ingress or vermin damage.
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4. Check power quality first.
Three phase supply should be present and balanced. Confirm neutral and earth. Record voltage readings before board diagnosis.
Three phase supply should be present and balanced. Confirm neutral and earth. Record voltage readings before board diagnosis.
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5. Split the fault by error family.
Use the buttons at the top: communication, remote, thermistors, pressure, fan, inverter/IPM, refrigeration or pump down.
Use the buttons at the top: communication, remote, thermistors, pressure, fan, inverter/IPM, refrigeration or pump down.
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6. Evidence before parts.
Record readings, photos of PCB plugs, error display, thermistor/pressure/fan tests and site conditions in the Freshdesk ticket.
Record readings, photos of PCB plugs, error display, thermistor/pressure/fan tests and site conditions in the Freshdesk ticket.
5. Wired remote signal test
3-wire remote signal expected readings: Y1 to Y3 should be 12V DC, no less than 11.4V DC. With Y2 removed, test between the disconnected Y2 cable going to the indoor and Y3: fluctuating 7-11/12V DC. Test between Y2 and Y3 at the remote terminals: fluctuating 7-11/12V DC.
E00 / wired remote controller flow
Confirm whether the fault appears on the wired remote, indoor LEDs, or both.
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Remove the remote from the wall base if required and access Y1/Y2/Y3. Do not short terminals.
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Check Y1 to Y3: expected 12V DC, no less than 11.4V DC. If missing, suspect indoor controller supply / controller PCB.
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Disconnect Y2 from the remote. Check disconnected Y2 wire to Y3: expected fluctuating 7-11/12V DC pulse from the indoor side.
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Check Y2 to Y3 at the remote controller terminals: expected fluctuating 7-11/12V DC pulse from the remote side.
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If one side has no pulse, isolate whether the remote controller, cable, or indoor controller PCB is the source. Record readings before replacing parts.
E01 / E13 communication split flow
E01 / E13 or no indoor / outdoor communication
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Isolate supply, remove outdoor terminal 3 signal wire, secure loose conductor, then re-energise safely
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Indoor side signal check Is indoor signal present?
| Outdoor side signal check Is outdoor signal present?
|
Important: No indoor signal leads to indoor fan motor checks. No outdoor signal leads to outdoor fan disconnection, outdoor serial re-check, and the outdoor component checks before approving the outdoor controller PCB.
7. Power checks and inverter voltage flow
High voltage warning: three phase AC input and DC bus testing must only be completed by a competent technician. DC bus can be approximately 560-600V DC on a three phase inverter circuit.
| Test point | Expected reading / action |
|---|---|
| Outdoor supply | Confirm 415V AC phase-to-phase and approximately 240V AC phase-to-neutral/earth. Check for missing phase, neutral issue, low voltage or imbalance. |
| Inverter DC bus | Three phase bridge rectifier DC output should be approximately 560-600V DC. |
| Power supply frequency / E2A | Check ground, harmonic/noise sources, supply at terminals and indoor/outdoor connections. Manual supply check references AC198-264V phase-to-neutral range. |
| Main to inverter communication / E2E | Check low voltage DC supply and communication harness between Main PCB and Inverter PCB. Inspect plug seating and contamination. |
E19 / E2A / E2E power flow
Confirm the exact error code and whether the breaker trips, unit powers up, display operates, or error only appears on compressor start.
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Inspect for water ingress, vermin, burnt components, swollen capacitors, loose plugs and signs of previous arcing.
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Confirm three phase input is present, balanced and within range. Record L1-L2, L2-L3, L1-L3 and each phase to neutral/earth.
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If AC input is correct, check DC bus output at the inverter/diode bridge circuit. Expected three phase DC output is approximately 560-600V DC.
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If DC bus is missing or abnormal, isolate and test diode bridge and inverter board with power off.
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If power and DC bus are correct but E2E remains, inspect Main PCB to Inverter PCB communication and 13V/5V low voltage supplies before recommending a PCB.
8. Fan motor testing
Fan motor caution: do not disconnect or reconnect a DC fan motor while power is applied. Internal fan motor PCB damage can also damage the controller PCB.
| DC fan motor wire / test | Expected reading |
|---|---|
| Power-on supply | High voltage DC on red/black circuit generally 330-380V DC. Control power white/black generally 15V DC. |
| Diode test: red lead RED, black lead BLACK | O/L |
| Diode test: red lead RED, black lead WHITE | 0.5V-1.8V, readings vary by motor generation. |
| Diode test: red lead BLACK, black lead RED | 0.8V-1.1V |
| Diode test: red lead BLACK, black lead WHITE | 0.4V-0.6V |
| Mechanical check | Fan shaft must rotate freely. Check seized bearing, obstruction, loose fan, damaged blade and motor overheating. |
E1b / indoor fan motor fault flow
Power off. Confirm the fan wheel/propeller rotates freely and there is no obstruction, bearing noise or loose lock nut.
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Inspect plug, harness, corrosion and moisture. Confirm fan motor has not been disconnected while powered.
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If safe and required, check power-on supply to the fan motor: high voltage DC and 15V DC control supply.
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Power off and unplug fan motor. Complete diode test using the expected values table above.
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If motor readings are short/open or shaft is seized, replace the fan motor. If motor tests OK but board output is missing, investigate controller/power PCB.
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Record readings, fan movement and plug photos in the ticket.
9. Thermistor testing
Thermistor principle: powered test is 5V DC feed from PCB and return voltage below 5V DC. Power-off test is resistance in kΩ with the thermistor unplugged. Compare bulb temperature to the relevant resistance chart.
| Thermistor at 20°C from training reference | Approx. resistance / DC return |
|---|---|
| Room temperature | 12.53kΩ / 2.21V |
| Indoor unit heat exchanger | 62.90kΩ / 2.21V |
| Discharge temperature | 64.50kΩ / 0.83V |
| Compressor temperature | 62.55kΩ / 0.86V |
| Outdoor unit heat exchanger | 6.10kΩ / 2.18V |
| Outdoor temperature | 12.64kΩ / 3.75V |
| Heat sink temperature | 6.10kΩ / 2.18V |
Thermistor error flow
Identify the exact thermistor code and physical sensor: room, indoor HEX, outdoor HEX, outdoor ambient, discharge pipe, heatsink or compressor.
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Power off. Check connector is not removed, misconnected, corroded or pulled tight. Check cable is not pinched or open.
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Remove connector and check thermistor resistance. Compare the reading against actual bulb temperature and the service chart.
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Power on only if safe. Check PCB supply at thermistor circuit: 5V DC feed and return voltage below 5V DC.
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If thermistor is open/shorted/out of range, replace thermistor. If 5V supply is missing with wiring confirmed, investigate the relevant PCB.
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If thermistor is physically off the pipe/holder, refit correctly and retest before recommending parts.
10. Pressure sensor and pressure switch testing
| Pressure sensor test | Expected reading / action |
|---|---|
| Power-on supply | Red to Black = 5V DC ±5% at Main PCB side connector. |
| Power-on return | Black to White = pressure return voltage. Training tip: discharge pressure voltage is approximately equal to pressure in kPa, e.g. 2.5V ≈ 2500kPa. |
| Manual HP/LP sensor graph | High pressure output range shown roughly 0.5V to 4.5V over 0-5MPa; low pressure graph roughly 0.5V to 3.5V over 0-1.7MPa. |
| Pressure switch | Continuity check. Pressure switch opens around 4.2 ±0.1MPa. |
| Power-off diode: black lead BLACK to red lead WHITE | 1.0V-1.1V |
| Power-off diode: black lead BLACK to red lead RED | 1.2V-1.3V |
| Power-off diode: black lead WHITE to red lead RED | 1.6V-1.7V |
| Power-off diode: black lead WHITE to red lead BLACK | 0.6V-0.7V |
| Power-off diode: black lead RED to red lead BLACK | 0.5V-0.6V |
| Power-off diode: black lead RED to red lead WHITE | 0.6V-0.7V |
| Earth to red/white/black | O/L |
E16 pressure sensor / switch flow
Check sensor and switch connectors: loose terminal, removed connector, wrong connection, damaged cable or corrosion.
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Power on if safe. Measure 1 pin red to 3 pin black: expected 5V DC ±5%. If missing, suspect Main PCB supply after wiring is confirmed.
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Measure 2 pin white to 3 pin black: compare return voltage to actual system pressure. If inconsistent, suspect pressure sensor or refrigerant condition.
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Check pressure switch continuity. Pressure switch operates around 4.2MPa. If incorrect, replace pressure switch after confirming actual pressure.
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Power off and unplug sensor for diode checks if required. Compare against the diode table.
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Do not replace a sensor until actual refrigeration pressure has been considered.
11. Electronic expansion valve testing
Model control reference: this service instruction states the EEV pulse range is 50-480 pulses in cooling/dry and 40-480 pulses in heating. The EEV is set to 480 pulses when the compressor stops and initialises by closing pulses at power-on or after long stop periods.
| EEV coil type | Expected resistance / action |
|---|---|
| 5-wire 12V coil | Red to White, Orange, Yellow and Blue: 45Ω-50Ω. All wires to earth: O/L. |
| 6-wire 12V coil | Red to White and Orange: 45Ω-50Ω. Brown to Yellow and Blue: 45Ω-50Ω. All wires to earth: O/L. |
| Physical check | Check coil is clipped down firmly, seated on valve body and no corrosion under the coil. |
| Refrigeration check | If EEV or strainer is restricted, symptoms can include low pressure, discharge temp and poor performance. Verify valves and charge before parts. |
EEV / strainer flow
Power off. Inspect EEV coil seating, clip, corrosion, harness and plug condition.
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Confirm whether coil is 5-wire or 6-wire, then complete resistance checks using the table above.
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Check all coil wires to earth. Expected O/L. Any short to earth is abnormal.
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If coil tests OK but symptoms suggest restriction, check operating pressures, temperature split, valve positions, strainer restriction and refrigerant charge.
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If replacing coil, ensure correct seating and retest operation before closing the job.
E1A compressor motor control flow - Outdoor unit
E1A compressor location detection / compressor start control concern
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Turn unit on and confirm whether abnormal compressor noise is present
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Abnormal compressor noise present Record noise evidence and confirm compressor / harness checks before recommending compressor. | Harness burnt, loose, open or mis-wired Repair/replace affected harness or terminal connection, then reset power and retest. | Compressor winding abnormal or insulation failed Escalate as compressor fault after values are recorded. | IPM diode path abnormal Escalate as IPM / inverter board fault after values are recorded. |
Important: The compressor harness and terminals must be physically inspected because the harness can burn, overheat or lose connection. Do not move directly to inverter PCB replacement without recording harness condition, compressor winding resistance and IPM diode readings.
E17 IPM / trip detection flow - Outdoor unit
E17 IPM / inverter protection after compressor start or protection stop
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Harness burnt or loose connection found Repair or replace affected harness or terminal connection. Do not fit PCB until connection integrity is restored. | Compressor winding value abnormal or insulation failed Escalate as compressor fault after values are recorded. | IPM diode path abnormal Escalate as IPM / inverter board fault after values are recorded. |
Important: For IPM/inverter protection, do not jump straight to inverter PCB replacement. Check airflow and heat exchanger condition first, then prove compressor harness connection, compressor winding resistance and IPM diode readings.
14. Diode bridge testing
| 3 phase diode bridge test | Expected reading |
|---|---|
| Power on AC input | L1-L2, L2-L3 and L1-L3 approximately 415V AC. |
| Power on DC output | Positive to negative approximately 560-600V DC. |
| Black lead +, red lead AC1 / AC2 / AC3 | Approximately 0.4V each. |
| Black lead AC1 / AC2 / AC3, red lead - | Approximately 0.4V each. |
| Black lead +, red lead - | 0.7-0.9V |
| Black lead -, red lead + | O/L |
Inverter voltage / diode bridge flow
Verify AC supply first. Do not diagnose diode bridge with missing phase or unstable supply.
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If AC input is present but DC output is missing or low, isolate power and wait for discharge.
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Disconnect relevant control harnesses before diode testing.
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Complete the diode bridge checks using the table above.
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If diode bridge is abnormal, replace the relevant inverter board/bridge assembly and apply heatsink paste correctly where required.
E0F discharge temperature error flow - Outdoor unit
E0F discharge temperature protection after compressor operation
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Primary check: suspect refrigerant leak / insufficient refrigerant first
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Check 3-way / service valves are fully open
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Leak or insufficient refrigerant found Repair leak, pressure test, evacuate and weigh in charge as required. | 3-way valve closed / not fully open Open valve fully and re-test operation. | EEV / capillary / strainer issue Confirm coil resistance, seating, operation noise and temperature difference across restriction. | Discharge thermistor abnormal Replace thermistor / repair harness only after value is confirmed against temperature. | All checks pass but E0F remains Main PCB becomes suspect after refrigerant, valves, EEV, airflow and thermistor are proven. |
Important: Treat discharge temperature as a refrigerant / system condition fault first. The most common cause is refrigerant leak or insufficient refrigerant. Do not recommend main PCB until the refrigerant circuit, service valves, EEV/strainer, outdoor fan/heat exchanger and discharge thermistor have been checked and recorded.
16. Low pressure flow
Manual low pressure reference: low pressure protection reduces compressor speed at low pressure and can stop the compressor if pressure remains very low. Low pressure error is linked to low refrigerant, sensor fault, valves, EEV/strainer or restriction.
E2F low pressure flow
Confirm actual low-side pressure and compare against pressure sensor return voltage.
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Check pressure sensor connector and 5V supply. Do not assume low refrigerant until sensor output is validated.
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Check for gas leak or insufficient charge. Correct leak, evacuate and recharge specified amount if required.
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Check gas and liquid valves are fully open.
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Check EEV and strainer for restriction or coil failure.
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Check indoor/outdoor airflow and coil condition because poor heat exchange can drive abnormal pressures.
17. High pressure flow
Manual high pressure reference: excessive high pressure protection operates when high pressure becomes excessive. Cooling pressure over-rise control reduces compressor speed above the control threshold and stops at the abnormal stop threshold.
E24 excessive high pressure flow
Check outdoor airflow first: dirty coil, blocked discharge, recirculation, fan speed, fan motor and installation clearances.
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Check pressure sensor return voltage against actual gauge pressure.
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Check for overcharge or non-condensables if recent service work was completed.
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Check EEV operation and strainer restriction. Confirm valve positions.
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In heating, check indoor airflow/duct/filter restrictions and indoor heat exchanger temperature rise.
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Only after airflow, pressure sensor and refrigerant charge are confirmed should PCB or refrigerant circuit components be considered.
18. Pump down and E98
Pump down / E98 flow
Confirm liquid and gas service valves are fully open before starting pump down.
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Hold PUMP DOWN button for more than 3 seconds. Compressor and outdoor fan start automatically; indoor fan also starts.
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When outdoor display shows rUn after approximately 5 minutes, close the liquid valve immediately.
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When the display changes after approximately 2-7 minutes, close the gas valve immediately.
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After End displays, compressor and outdoor fan stop automatically after about 1 minute. Turn power off.
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If E98 pump down error occurs, recover refrigerant from the service port rather than repeating blindly.
19. Freshdesk ticket evidence checklist
| Evidence item | Record in ticket |
|---|---|
| Error proof | Photo of wired remote error and outdoor 7-segment display / error history. |
| Safety and access | Confirm licensed/competent agent, isolation, PPE, safe access, no customer electrical work. |
| Model details | Indoor/outdoor model and serial, installation date, refrigerant type, pipe length if known. |
| Power readings | Supply voltage, phase-to-phase, phase-to-neutral/earth, DC bus where applicable. |
| Component readings | Thermistor kΩ/voltage, fan diode values, pressure sensor voltage, EEV resistance, compressor resistance/megger, IPM/bridge diode values. |
| Site conditions | Filters, coils, airflow, ductwork, outdoor clearance, valves open, signs of leak, water ingress, vermin or corrosion. |
| Decision | Part recommended, why, and what readings support it. If not enough evidence, request further tests rather than guessing. |