Component Testing - Technician Quick Reference
Diagnostic test procedures for electrical fault isolation and component verification in Fujitsu inverter and standard air conditioning systems.
Electrical safety warning
Testing must only be completed by appropriately qualified technicians. Isolate the power supply before resistance or diode testing. Live-voltage testing exposes the technician to hazardous voltages, including DC bus voltages up to 380 V DC.
Purpose
This guide provides a structured overview of diagnostic test procedures for key components. It is intended as a quick reference for technicians performing on-site electrical testing, fault isolation and verification of component operation.
Before testing
- Confirm whether the test is a power-off resistance/diode check or a power-on voltage check.
- Verify readings against ambient temperature, particularly for thermistors and motors.
- Use model-specific service data where available.
- Cross-check unexpected readings using the Mobile Technician App.
Quick reference values
| Component | Test | Expected reading |
|---|---|---|
| Diode bridge | Diode test | Approx. 0.4 V per diode; 0.7-0.9 V between + and - |
| Active Filter Module (ACTPM) | Resistance | 360 kΩ-900 kΩ between terminals |
| Intelligent Power Module (IPM) | Diode test by phase | 0.4 V ± 0.1 V per phase |
| DC brushless fan motor | Diode test | White-to-black: 0.5-1.8 V; black-to-red: 0.8-1.1 V |
| AC fan motor | Phase resistance | Typically 5-20 Ω; use the fan-specific table |
| Pressure transducer | Powered voltage test | 5 V DC supply; 0.5-4.5 V return proportional to pressure |
| EEV coil - standard | Resistance | 45-50 Ω between control wires |
| EEV coil - J Series | Resistance | Approx. 150 Ω per winding |
1. Signal communication tests
Use signal testing to verify communication between indoor and outdoor units and to assess the three-wire remote controller circuit at terminals Y1, Y2 and Y3.
- Check the system signal between the indoor and outdoor units.
- Check the three-wire remote controller signal at Y1, Y2 and Y3.
- Compare measured DC serial communication voltages with the applicable indoor and outdoor circuit data.
2. Power conversion and drive components
Diode bridge - single-phase and three-phase
The diode bridge converts the incoming AC supply to DC voltage.
- Expected forward voltage drop: approximately 0.4 V per diode.
- Expected reading between the positive and negative terminals: 0.7-0.9 V.
Active Filter Module (ACTPM)
The ACTPM improves power factor and supplies the DC bus to the inverter.
- Expected resistance between terminals: 360 kΩ-900 kΩ.
Intelligent Power Module (IPM)
The IPM drives the compressor windings at U, V and W.
- Expected diode reading: 0.4 V ± 0.1 V per phase.
3. Fan motor testing
DC brushless fan motors
These motors operate with approximately 330-380 V DC main power and 15 V DC control power.
- White-to-black diode reading: 0.5-1.8 V.
- Black-to-red diode reading: 0.8-1.1 V.
AC fan motors
Check resistance across the phases and compare the result with the fan-specific table. A typical range is 5-20 Ω.
4. Sensor testing
Thermistors
| Test condition | Method and expected result |
|---|---|
| Power on | Expect a 5 V DC supply and a lower return voltage that varies with temperature. |
| Power off | Measure resistance and compare it with the applicable thermistor table or the Mobile Technician App. |
Pressure transducer
- Expected supply between red and black: 5 V DC.
- Expected return signal: 0.5-4.5 V, proportional to system pressure.
5. Electronic Expansion Valve (EEV) coil testing
- Five-wire and six-wire coils: 45-50 Ω between control wires.
- J Series high-resistance coils: approximately 150 Ω per winding.
- Coil-to-earth test: O/L is expected.
6. Thermistor reference at 20°C
| Sensor | Reference resistance |
|---|---|
| Room temperature thermistor | 12.5 kΩ |
| Heat exchanger thermistor | 62.9 kΩ |
| Compressor thermistor | 62.5 kΩ |
A typical thermistor signal voltage at 20°C is 2.1-2.3 V DC.
7. Manual test run from the outdoor display
- Use the outdoor LED display board to start a manual test run when wall controller access is unavailable.
- After testing, terminate the test run at the outdoor display so control is returned to the wall controller.
Interpreting abnormal readings
Readings outside the expected range may indicate a shorted diode, open circuit, failed component or PCB fault. Confirm the reading, test under the correct power condition and compare it with the applicable model-specific service information before replacing parts.