General Assist Technical Reference
Air Conditioning Component Test Sheets
Electrical, communication, inverter, sensor and actuator checks
Reference readings for qualified Fujitsu air conditioning service technicians
These test sheets consolidate typical readings used to assess communication circuits, inverter power components, fan motors, thermistors, electronic expansion valves and pressure transducers before parts are replaced.
Electrical safety: Testing may involve 240 V AC, 400–415 V AC and DC voltages up to approximately 600 V. Work must only be completed by appropriately licensed and competent personnel. Isolate and prove the supply is de-energised before disconnecting plugs or completing resistance and diode tests. Allow DC bus capacitors to discharge.
Model-specific values take priority: These are general reference values. Confirm terminal identification, connector pinout and expected readings in the service manual for the exact indoor and outdoor model before condemning a component.
1. Communication and signal tests
Indoor-to-outdoor serial signal
Measure DC voltage between terminal 2 (neutral) and terminal 3 (signal). To separate indoor and outdoor signals, disconnect terminal 3 and test each side independently. Cross-check from both ends before concluding the interconnecting cable or PCB is faulty.
| Model group | Indoor signal | Outdoor signal |
|---|---|---|
| AST and ART/C | 60–120 V DC | 60–120 V DC |
| ASTA and ASTB | 40–90 V DC | 40–90 V DC |
| ASTG | Approx. 200 V DC static | 3–110 V DC |
| ARTG and three-phase | Approx. 295 V DC static | 3–110 V DC |
Three-wire remote controller
| Test | Expected reading | Interpretation |
|---|---|---|
| Y1 to Y3 | 12 V DC; not less than approximately 11.4 V DC | Controller supply. Missing voltage may indicate a controller-board or wiring fault. |
| Y3 to Y2 | Fluctuating 7–11 V DC pulse | Communication pulse at the controller terminals. |
| Y3 to disconnected Y2 cable | Fluctuating 7–11 V DC pulse | Communication pulse from the indoor unit. |
2. Typical outdoor PCB voltage checks
| Circuit | Typical reading | Notes |
|---|---|---|
| Main PCB DC input | 330–370 V DC | High-voltage DC bus supply. |
| Outdoor fan motor | Red–black: 330–370 V DC White–black: 15 V DC | Do not unplug the motor while energised. |
| EEV coil supply | 12 V DC | Check only using the applicable model procedure. |
| Thermistor supply | 5 V DC | Return voltage varies with temperature. |
| High-pressure sensor supply | 5 V DC | Return voltage corresponds to pressure. |
| Reversing-valve solenoid | 240 V AC | Shown energised in heating mode on the reference PCB. |
3. Power conversion and inverter components
ACTPM active filter module — power OFF
Disconnect all control harnesses and measure resistance on auto-range. A shorted ACTPM may trip the supply circuit breaker.
| Black lead | Red lead | Expected |
|---|---|---|
| − | + | 360 kΩ |
| L1 | 360 kΩ | |
| L2 | Over 1 MΩ | |
| N | 0 Ω | |
| + | P | 720–900 kΩ |
| N | P | 360–540 kΩ |
IPM / transistor PCB — power OFF, diode mode
| Black lead | Red lead | Expected |
|---|---|---|
| P | U | 0.4 V |
| V | 0.4 V | |
| W | 0.4 V | |
| U / V / W | N | 0.4 V each |
| P | N | 0.7–0.9 V |
| N | P | OL |
Bridge rectifier
| Test condition | Expected reading |
|---|---|
| Single-phase, power OFF, diode mode | + to each AC terminal: 0.4 V; each AC terminal to −: 0.4 V; + to −: 0.7–0.9 V; reverse − to +: OL. |
| Three-phase, power ON | L1–L2, L2–L3 and L1–L3: 400–415 V AC. Each phase to neutral/earth: 230–240 V AC. DC − to +: 560–600 V DC. |
| Three-phase, power OFF, diode mode | + to each AC phase: 0.4 V; each AC phase to −: 0.4 V; + to −: 0.7–0.9 V; reverse − to +: OL. |
4. DC brushless fan motor — power OFF
Do not disconnect the fan motor while power is applied. The motor contains an internal electronic circuit and operates from a high-voltage DC supply.
| Red lead | Black lead | Expected |
|---|---|---|
| Red | Black | OL |
| White | Black | 0.5–1.8 V |
| Black | Red | 0.8–1.1 V |
| Black | White | 0.4–0.6 V |
Also check that the shaft rotates freely and is not partially or fully seized. Older motors may read near 0.5 V from white to black, while newer motors may read near 1.8 V.
5. Thermistors and pressure transducers
Thermistor testing
- Power ON: one side of the thermistor circuit should have approximately 5 V DC to DC ground. The return side should be below 5 V DC and varies with temperature.
- Power OFF: unplug the thermistor and measure resistance in kΩ. Compare bulb temperature, resistance and return voltage with the model-specific chart.
- Inspect the bulb and cable for damage and test for a short to earth.
| Thermistor at 20°C | Resistance | Return voltage |
|---|---|---|
| Room temperature | 12.535 kΩ | 2.219 V DC |
| Indoor heat exchanger | 62.905 kΩ | 2.212 V DC |
| Discharge temperature | 64.501 kΩ | 0.839 V DC |
| Compressor temperature | 62.550 kΩ | 0.860 V DC |
| Outdoor heat exchanger | 6.100 kΩ | 2.189 V DC |
| Outdoor ambient | 12.643 kΩ | 3.759 V DC |
Pressure transducer
Power ON: red to black should be approximately 5 V DC. Black to white is the return voltage. As an approximate example, a 2.8 V DC discharge-pressure return corresponds to about 2875 kPa.
| Black lead | Red lead | Power-OFF diode reading |
|---|---|---|
| Black | White | 1.0–1.1 V |
| Black | Red | 1.2–1.3 V |
| White | Red | 1.6–1.7 V |
| White | Black | 0.6–0.7 V |
| Red | Black | 0.5–0.6 V |
| Red | White | 0.6–0.7 V |
| Earth | Red / white / black | OL |
6. Electronic expansion valve coil tests — power OFF
| Coil type | Test pairs | Expected |
|---|---|---|
| 5-wire, 12 V | Red to white, orange, yellow and blue | 45–50 Ω each |
| 6-wire, 12 V | Red to white and orange; brown to yellow and blue | 45–50 Ω each |
| J-series high-resistance 6-wire | Red to white and orange; brown to yellow and blue | 150 Ω each; blue–yellow and orange–white approximately 300 Ω |
| All coil types to earth | Every conductor to earth | OL |
Inspect for corrosion beneath the coil and confirm the coil is correctly located and firmly clipped to the valve body.
7. Multi-head inverter signal chips
| Black lead | Red lead | Expected resistance |
|---|---|---|
| Neutral | Signal A | 1.5–2 MΩ |
| Signal B | 1.5–2 MΩ | |
| Signal C | 1.5–2 MΩ | |
| Signal D | 1.5–2 MΩ |
8. Outdoor-board test run
Where the wall controller is unavailable, some models allow a test run to be initiated from the outdoor LED display board. Use the switch sequence and LED interpretation in the service manual for the exact model.
Return control after testing: Stop the test run from the outdoor display board when testing is complete. Outdoor-board test operation overrides the wall controller until it is cancelled.
9. Diagnostic workflow
- Record the complete indoor and outdoor model numbers, serial numbers and fault history.
- Confirm the supply voltage, earthing, phase condition and protective devices.
- Inspect boards, harnesses and connectors for heat damage, moisture, corrosion or loose connections.
- Use the exact meter mode and lead polarity shown for the test.
- Compare all readings with the applicable service manual, not one isolated reading.
- Confirm related loads are not shorted before fitting a replacement PCB.
- After repair, restore all covers and earth connections, then complete a controlled test run.
Important: A correct static component reading does not prove the entire system is operating correctly. Continue diagnosis where supply, communication, mechanical or load-related faults remain possible.