AIRSTAGE Technical Reference
Fujitsu Component Testing
Electrical diagnostic procedures and expected readings
Quick reference for qualified technicians testing inverter and standard air conditioning systems
This guide provides a structured overview of diagnostic test procedures for key components within Fujitsu inverter and standard air conditioning systems. Use it as a quick reference when performing on-site electrical testing, fault isolation and component verification.
Electrical safety: Testing must only be completed by appropriately qualified personnel. Isolate power before resistance or diode tests. Power-on voltage testing involves hazardous voltages, including DC bus voltages up to 380 V DC.
1. Signal communication tests
- Verify the system communication signal between the indoor and outdoor units.
- For a 3-wire remote controller, test the signal at terminals Y1, Y2 and Y3.
- Confirm the expected DC serial communication voltage values at both the indoor and outdoor circuits.
Diagnostic approach: Confirm supply and polarity first, then compare the measured signal against the applicable model documentation. A missing or unstable signal may indicate wiring, connection or PCB issues.
2. Power conversion and drive components
| Component | Function | Expected reading |
|---|---|---|
| Diode bridge 1-phase / 3-phase | Converts the AC supply to DC voltage. | Approximately 0.4 V forward voltage drop per diode; 0.7–0.9 V between positive and negative. |
| Active Filter Module (ACTPM) | Improves power factor and supplies the DC bus to the inverter. | Resistance range: 360 kΩ–900 kΩ between terminals. |
| Intelligent Power Module (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
| Motor type | Supply / test | Expected reading |
|---|---|---|
| DC brushless motor | Typically operates with 330–380 V DC main power and 15 V DC control power. | White-to-black: 0.5–1.8 V diode reading. Black-to-red: 0.8–1.1 V diode reading. |
| AC fan motor | Check resistance across the motor phases. | Refer to the fan-specific table; the typical range is 5–20 Ω. |
4. Sensor testing
Thermistors
- Power on: Expect a 5 V DC supply with a lower return voltage. The return voltage varies with temperature.
- Power off: Check resistance against the applicable thermistor table or the Mobile Technician App.
Pressure transducer
- Confirm 5 V DC between the red and black wires.
- Expected return signal is 0.5–4.5 V DC, proportional to system pressure.
5. Electronic expansion valve coil testing
| Coil type | Expected resistance | Additional check |
|---|---|---|
| 5-wire / 6-wire coil | 45–50 Ω between control wires. | Test each winding and compare readings for consistency. |
| J Series high-resistance coil | Approximately 150 Ω per winding. | Always test the coil to earth; the expected result is O/L. |
6. Thermistor quick reference at 20°C
| Thermistor | Typical resistance at 20°C | Typical voltage at 20°C |
|---|---|---|
| Room temperature | 12.5 kΩ | Typically 2.1–2.3 V DC. Confirm against the applicable sensor table. |
| Heat exchanger | 62.9 kΩ | |
| Compressor | 62.5 kΩ |
Thermistor readings are temperature-dependent. Compare the measured resistance with the actual sensor temperature rather than relying on the 20°C reference alone.
7. Manual test run procedure
- Where wall controller access is unavailable, activate the manual test run from the outdoor unit LED display board.
- Observe system operation and complete the required diagnostic checks.
- Terminate the test run from the outdoor display when testing is complete. This returns operating control to the wall controller.
8. Technician notes
- Always isolate power before performing resistance or diode tests.
- Verify readings against ambient or component temperature, particularly for thermistors and motors.
- Cross-check unusual readings using the Mobile Technician App and the applicable model documentation.
- Abnormal readings may indicate shorted diodes, open circuits, damaged wiring, a failed component or PCB failure.
Important: The values in this article are a quick reference only. Model-specific service documentation takes priority where values or test methods differ.