ASTH Single Phase Wall Hung Split Systems

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 person onsite is authorised, has PPE and suitable test equipment. For power-off tests, isolate supply and wait before touching electrical components. Do not instruct a customer or unqualified person to remove covers or perform electrical tests.
Scope note: This wall hung article intentionally does not include a 3 wire wall-controller flow because these ASTH wall hung split systems are normally controlled by wireless remote rather than a 3 wire wired controller.

1. Document scope

AreaDetails
Product familyASTH single phase wall hung split systems
Controller typeWireless remote controller. No 3 wire wall-controller flow included.
Core support focusIndoor LED fault display, indoor/outdoor communication, DC brushless fan motors, main controller PCB power-on/off tests, diode bridge/IPM, thermistors, EEV, compressor and refrigerant checks.
Component training items includedDC brushless fan motor: 330-380 VDC high voltage, 15 VDC control, feedback/speed signal; diode test preferred over resistance for fan motor electronics; do not disconnect fan motor with power applied.
PurposeFreshdesk-ready call guide with linked navigation, GREAT-style flowcharts, expected readings and ticket evidence requirements.

2. Error / fault map

Fault familyLikely service-manual wordingPhone support action / linked test
Indoor LED error displayOperation / Timer / Economy flash patternIndoor LED display flow
Communication faultIndoor / outdoor serial communication errorCommunication split flow
Indoor fan faultIndoor unit fan motor errorIndoor fan motor flow
Outdoor fan faultOutdoor unit fan motor errorOutdoor fan motor flow
Thermistor faultRoom, indoor heat exchanger, outdoor, discharge, heat exchanger or compressor thermistor errorThermistor testing
IPM / inverter faultIPM error, inverter error, active filter / main PCB protectionIPM / main PCB flow
Compressor control faultCompressor motor control, rotor detection or start-up faultCompressor control flow
Discharge temperature faultDischarge temperature protection after compressor operationDischarge temperature flow
Refrigerant / EEV / restrictionLow pressure, insufficient refrigerant, EEV or strainer restrictionRefrigerant / EEV flow

3. Quick map

Symptom / error familyMost likely areaJump to
LEDs flashing but customer cannot describe codeOperation / Timer / Economy flash pattern and status tableLED identification
No communication / communication errorTerminal wiring, signal, earth/noise, fan motor loading, indoor/outdoor PCBCommunication
Indoor fan motor errorFan rotation, bearing, motor winding/electronics, controller PCBIndoor fan
Outdoor fan motor errorDC brushless fan, high voltage DC, 15 VDC control, diode test, PCB outputOutdoor fan
IPM / inverter errorDiode bridge, fuses, compressor winding, main PCB, IPM outputIPM / main PCB
Compressor errorHarness, U/V/W winding resistance, abnormal compressor noise, IPM/main PCBCompressor
Discharge temperature faultRefrigerant leak/undercharge, 3-way valve, EEV/strainer, fan/coil, thermistorDischarge temp
Thermistor faultSensor connector, resistance at actual temperature, 5 V PCB supplyThermistors

4. Indoor unit LED display guidance

LED itemFreshdesk instruction
Lamp namesRecord the condition of Operation, Timer and Economy / Filter indicators. Colours vary by model and age.
Error displayThe indoor unit LEDs display a flash pattern when in fault. In some cases the unit must be turned on by the remote for the code to show.
Do not misclassify status lightsDefrost, filter notification, demand response, timer setting errors, test run and restricted function can display LED states that are not component faults.
EvidenceAsk for a photo or short video of the LEDs and record flash count, LED colour and whether each lamp is off, on, blinking, fast blinking or any-state.

5. GREAT-style linked flowcharts

Indoor unit LED display flow - ASTH wall hung

Use the indoor LED pattern to confirm the active fault before moving to component testing
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Turn the unit on at the remote controller if the fault only displays during operation
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Identify lamp names and colours: OPERATION, TIMER and ECONOMY / FILTER. Colours can vary by model and generation.
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Count the flashes and confirm whether LEDs are off, on, blinking, fast blinking or any-state
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Error code display
Operation, timer and economy pattern indicates a fault. Match the pattern to the service manual error table.
Defrost / filter / demand / restricted function
Do not treat as a fault until the status table confirms it is an actual error code.
No LED or unclear pattern
Check power supply, remote operation and repeat fault history. Ask for video if needed.
Record in ticket: lamp names, colours, flash counts, whether the unit needed to be turned on for the code to display, and a photo/video if possible.

Communication error split flow - ASTH wall hung

Indoor / outdoor communication error or no serial signal
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Indoor side signal path
Indoor sends/receives signal correctly?
YES
Continue to outdoor signal path and outdoor PCB/fan loading checks.
NO
Check indoor fan motor and indoor controller PCB only after terminal and cable are proven.
Outdoor side signal path
Outdoor signal returns?
YES
Suspect intermittent cable/terminal/noise issue. Record readings and inspect plug connections.
NO
Disconnect outdoor fan motor(s) and re-check serial signal before approving outdoor PCB.
Important split: Do not approve an indoor or outdoor PCB on a communication fault until terminal wiring, polarity, cable continuity, earth/noise and fan motor loading have been checked and recorded.

Indoor fan motor error flow - ASTH wall hung

Indoor unit fan motor error / actual fan frequency below target
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Confirm the exact LED/error pattern and whether fault returns after reset
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Power off and rotate indoor fan by hand. Check fan barrel, bearings, casing contact, obstruction and dust build-up
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Check ambient temperature around fan motor and any surrounding heat source
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Check indoor fan motor using component testing method. Do not disconnect fan motor while power is applied
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If fan motor is abnormal, replace indoor fan motor. If fan motor tests OK and fault remains, indoor controller PCB becomes suspect
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Fan locked / bearing issue
Replace fan or bearing assembly and clean obstruction before PCB decision.
Motor abnormal
Replace indoor fan motor. If motor shorted or diode test abnormal, protect PCB decision as required.
Motor tests OK
Indoor controller PCB becomes suspect after wiring and fan motor are proven.
Overheat condition
Remove heat source / correct airflow and restart operation.
Important: For DC brushless fan motors, diode test is preferred. Resistance readings can be inconsistent and misleading because the motor has internal PCB circuitry.

Outdoor fan motor error flow - ASTH wall hung

Outdoor DC brushless fan motor error / outdoor fan feedback or speed error
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Power off. Visually inspect fan blade, guard, bearing, obstruction, water ingress and signs of motor damage
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Confirm the fan connector has not been disconnected with power applied
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Power off test: disconnect fan motor and perform diode test between DC ground, high voltage DC and control pins
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Power on test only if safe: verify high voltage DC supply and 15 VDC control supply at PCB side
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If fan motor is abnormal, replace outdoor fan motor. If fan motor is normal but PCB output is missing, main PCB becomes suspect
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Fan obstruction / blade issue
Clear obstruction or replace damaged fan parts before electrical approval.
Diode test abnormal
Outdoor fan motor is affecting signal/control. Replace fan motor and document results.
15 VDC / high DC missing
Main PCB output/fuse/drive section becomes suspect after input supply is confirmed.
All fan checks OK
Continue to PCB/IPM and communication checks before approving board.
Important: DC brushless fan motors operate on high voltage DC and 15 VDC control. Do not disconnect the fan motor with power applied.

IPM / main controller PCB flow - ASTH wall hung outdoor

IPM, inverter, active filter, diode bridge or main PCB protection fault
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Confirm L-N supply, earth condition and whether a breaker/fuse has tripped
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Inspect main controller PCB for burn marks, water ingress, vermin, cracked solder, loose connectors and silicone-gel contact issues
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Power on tests if safe: 240 VAC input, 240-280 VDC input, 330-380 VDC compressor/fan high voltage rail, 5/12/15 VDC control supplies
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Power off tests: fuse continuity, diode bridge diode test, IPM diode test and compressor winding resistance
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Do not replace PCB until compressor, fan motor, diode bridge, fuses and external supply are documented
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Fuse open
Check downstream load before replacing PCB or fuse. Record continuity result.
Diode bridge abnormal
Escalate diode bridge / main PCB repair decision with readings recorded.
IPM diode path abnormal
Escalate as IPM/main PCB fault after compressor winding is proven.
Supply/control voltages missing
Main PCB or power supply section suspect after input supply is confirmed.
Important: Boards may be coated in clear silicone gel. Ensure meter probes make solid contact to solder joints and do not rely on poor surface contact.

Compressor motor control flow - ASTH wall hung outdoor

Compressor start-up / rotor detection / motor control error
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Turn unit on and confirm whether abnormal compressor noise is present
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Isolate supply and visually inspect compressor harness, U/V/W terminals and PCB solder connections
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Check compressor winding resistance U-V, V-W and U-W. Values should be balanced and not 0 ohm or open circuit
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Check IPM diode path and power PCB/main PCB drive section
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If compressor winding is abnormal, escalate compressor. If winding is normal but IPM path is abnormal, escalate PCB/IPM
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Abnormal compressor noise
Record noise evidence and complete harness/winding/IPM checks before compressor approval.
Harness burnt, loose or miswired
Repair or replace harness/terminal, then reset and retest.
Winding abnormal
Escalate as compressor fault after all three winding values are recorded.
IPM abnormal / windings OK
Escalate as IPM/main PCB fault with compressor readings attached.
Important: Do not approve a compressor or PCB without recording U-V, V-W, U-W resistance, harness condition and IPM diode readings.

Discharge temperature error flow - ASTH wall hung outdoor

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 valves are fully open and caps are fitted
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Check EEV operation / coil resistance, capillary tube and strainer restriction
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Check outdoor fan operation and heat exchanger for foreign matter, blocked fins or recirculation
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Check discharge temperature thermistor value and DC return voltage
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Only after refrigerant, valve, EEV, airflow and thermistor checks are proven should PCB be considered
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Leak / insufficient refrigerant
Repair leak, pressure test, evacuate and weigh in charge as required.
3-way valve not fully open
Open valve fully and re-test operation.
EEV / strainer issue
Confirm coil resistance, start-up noise, operation and temperature difference across restriction.
Discharge thermistor abnormal
Replace thermistor or repair harness only after value is confirmed against temperature.
All checks pass
PCB becomes suspect after refrigerant circuit evidence is complete.
Important: The main cause to prove first is refrigerant leak or insufficient refrigerant. Do not jump directly to PCB replacement.

Refrigerant / EEV / low pressure support flow

Low pressure, poor performance, EEV restriction or refrigerant circuit fault
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Confirm mode, set point, fan speed, indoor return air, outdoor ambient and operating time
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Check filters, indoor coil, outdoor coil, fan operation and air recirculation
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Check pipe temperature split and signs of undercharge, restriction or moisture contamination
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Check EEV coil resistance, EEV drive voltage and start-up noise
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Check strainers for temperature difference and confirm valve positions
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Leak test, pressure test, evacuate and weigh in charge where refrigerant fault is proven
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Airflow issue
Correct filters, fan, coils or recirculation before refrigeration work.
EEV coil / drive abnormal
Record coil resistance and drive voltage before EEV or PCB recommendation.
Restriction indicated
Temperature difference across strainer/capillary supports restriction diagnosis.
Leak / undercharge
Repair leak and weigh in correct R410A charge.
Important: R410A must be charged as liquid with correct tools and weighing procedure. Do not gas-charge or top up blindly.

6. Step-by-step phone support SOPs

SOP 1 - Intake and safety gate

  1. Confirm caller name, company, site address, indoor model/serial and outdoor model/serial.
  2. Confirm exact symptom: LED pattern, mode, when it occurs and whether repeatable.
  3. Confirm safety: no burning smell, water ingress, damaged wiring, repeated breaker trips or refrigerant odour.
  4. Confirm tools: multimeter with AC/DC volts, resistance and diode test.
  5. If caller is not qualified or cannot safely identify terminals, stop at non-invasive checks and arrange authorised attendance.

SOP 2 - Indoor LED display

  1. Ask caller to turn the unit on with the wireless remote if no code is visible.
  2. Identify Operation, Timer and Economy/Filter LEDs. Record colour and position because colours vary by model.
  3. Record whether each LED is off, on, blinking, fast blinking or any-state.
  4. Separate status indications from fault indications: defrost, filter, demand response, timer setting error, test run and restricted function are not always component faults.
  5. Ask for a photo or short video of the flash sequence where possible.

SOP 3 - Indoor / outdoor communication

  1. Power off and inspect terminal 1/2/3 interconnect, L/N supply, earth and polarity.
  2. Check for loose terminal, open cable, water ingress, damaged conductor or incorrect cable termination.
  3. Check for external noise or harmonic source near power cable.
  4. Check indoor and outdoor signal at terminals as per model manual. Record AC/DC values and whether signal fluctuates.
  5. Disconnect outdoor fan motor(s) and re-check serial signal if outdoor signal is missing before approving outdoor PCB.
  6. If wiring and motor loading are proven normal, assess indoor/outdoor PCB based on where the signal is missing.

SOP 4 - Indoor fan motor

  1. Power off. Rotate fan barrel by hand and check obstruction, dropped fan, bearing, casing contact and dirt build-up.
  2. Check fan motor connector and harness.
  3. Check motor by diode test where DC brushless motor is fitted. Do not rely on resistance only.
  4. Do not disconnect or reconnect fan motor while power is applied.
  5. If fan motor is abnormal, replace fan motor and document whether PCB may also be affected by the motor fault.

SOP 5 - Outdoor DC brushless fan motor

  1. Power off. Rotate fan blade by hand and check bearing, obstruction, fan guard contact, weather damage and water ingress.
  2. Identify fan motor wires: feedback signal, speed signal, 15 VDC control, DC ground and high voltage DC.
  3. Power off diode test is required. Resistance reading can be inconsistent and misleading.
  4. Power on testing, if safe and qualified: check high voltage DC rail, 15 VDC control and feedback/speed signal at PCB side.
  5. Do not disconnect with power applied.

SOP 6 - Main controller PCB power on / power off tests

  1. Power on tests: confirm 240 VAC input, 240-280 VDC input, 330-380 VDC high voltage output and 5/12/15 VDC control supplies where applicable.
  2. Power off tests: fuse continuity, diode bridge diode test, IPM diode test, thermistor resistance, EEV coil resistance and compressor winding resistance.
  3. When PCB is coated with clear silicone gel, make firm probe contact to solder joints.
  4. Record all readings before board approval.

SOP 7 - IPM and diode bridge

  1. Power off and discharge safely before diode tests.
  2. Check diode bridge using diode mode, not resistance mode.
  3. Check IPM diode paths between P/N and U/V/W outputs.
  4. Check compressor winding balance before condemning IPM.
  5. If IPM path is abnormal and compressor winding is normal, escalate PCB/IPM decision with readings.

SOP 8 - Thermistors

  1. Isolate power. Check thermistor connector is not loose, removed, pinched, miswired or open.
  2. Disconnect thermistor and measure resistance out of circuit.
  3. Compare resistance to actual bulb temperature from the model service manual table.
  4. With thermistor removed, check PCB thermistor supply, commonly 5 VDC on many models.
  5. Replace thermistor only when open/short/out of table. Replace PCB only when sensor and wiring are proven.

SOP 9 - EEV coil / strainer

  1. Check EEV connector and cable for damage or loose connection.
  2. Power off and check EEV coil resistance between common and phase wires. Typical training reference is approximately 46 ohms plus/minus tolerance at 20C, but verify against the model manual.
  3. Power on restart and listen/feel for EEV initialisation noise.
  4. Check for temperature difference across strainer/capillary indicating restriction.
  5. If coil is normal but drive voltage is missing, PCB output becomes suspect.

SOP 10 - Compressor

  1. Power off. Inspect U/V/W compressor harness, terminal condition and PCB solder points.
  2. Check winding resistance U-V, V-W and U-W. Values should be balanced and not 0 ohm or open circuit.
  3. Check abnormal compressor noise only after confirming correct mode and demand.
  4. Check IPM diode path and high voltage DC rail before compressor/PCB approval.
  5. Record values and evidence before recommending compressor or PCB.

7. Ticket evidence checklist

Evidence requiredDetails to record
Model and serialIndoor and outdoor model/serial, controller type and exact LED/error display.
Safety and site conditionWho is onsite, licence/competency confirmation, isolation status, access limits, water ingress/burning smell/short circuit risk.
LED evidenceOperation / Timer / Economy or Filter LED colours, flash counts, fast/slow blink, photo/video and whether remote had to turn unit on.
Electrical readingsL-N supply, terminal communication values, PCB AC/DC rails, 15 VDC fan control, 5 V thermistor supply, fuse continuity, diode bridge and IPM diode results.
Component readingsFan motor diode result, thermistor kΩ and temperature, EEV coil Ω, compressor U/V/W winding Ω.
Refrigeration evidenceValve positions, mode, ambient, fan operation, coil condition, pressures, leak test, strainer temperature difference and weighed charge details.
Approval decisionState what has been proven before recommending remote, indoor PCB, outdoor PCB, fan motor, thermistor, EEV, compressor, diode bridge or IPM/main PCB.