AIRSTAGE Technical Reference
Active Filter Module (ACTPM) Resistance Testing
Power-off resistance checks for Active PFC / IPM modules
The Active Filter Module maintains power factor correction, regulates the DC bus and reduces harmonic distortion. Internal failure may cause immediate trips, repeated fuse failure, unstable DC voltage or PCB damage.
High-voltage hazard: Isolate all power for at least 10 minutes, verify capacitor discharge and disconnect all control and signal harnesses before testing. Use resistance measurements only. Do not perform continuity or megger testing on the module.
1. Function overview
The ACTPM regulates the DC bus and input line current through an integrated control circuit and insulated power transistors. It maintains voltage balance across the DC link and controls charging and discharging timing.
2. Terminal identification
| Terminal | Designation | Function |
|---|---|---|
| - (Black) | Negative DC bus | Common ground reference |
| + (Red) | Positive DC bus | DC power input |
| L1 (White) | AC line input | Power phase input 1 |
| L2 (Brown) | AC line input | Power phase input 2 |
| N / N1 (Blue) | Neutral output | DC-side control reference |
| P (Yellow) | DC positive output | Filtered DC voltage output |
3. Resistance test procedure
- Turn the system off, isolate all supplies and wait at least 10 minutes.
- Verify that the DC bus has discharged before touching terminals.
- Disconnect all control and signal harnesses from the ACTPM.
- Set the digital multimeter to auto-range resistance (kΩ).
- Identify the terminals from the ACTPM housing or schematic.
- Measure and record each connection listed below.
| Multimeter connection | Expected reading | Interpretation |
|---|---|---|
| Black (-) to Red (+) | 360 kΩ | Normal |
| Black (-) to L1 (White) | 360 kΩ | Normal |
| Black (-) to L2 (Brown) | Greater than 1 MΩ | Normal / high isolation |
| Black (-) to N (Blue) | 0 Ω | Common reference point |
| Red (+) to P (Yellow) | 720-900 kΩ | Normal range |
| N (Blue) to P (Yellow) | 360-540 kΩ | Normal range |
Important: Resistance values can vary with meter type, component charge state and module version. Confirm model-specific values where available and compare with a known serviceable unit when readings are borderline.
4. Evaluation
| Observation | Interpretation | Action |
|---|---|---|
| All readings within specification | ACTPM operating normally | No module replacement indicated |
| 0 Ω between + and - | Internal transistor short circuit | Replace ACTPM |
| Open circuit between N and P | Open internal connection | Replace ACTPM |
| Low resistance across multiple terminals | Internal diode or transistor breakdown | Replace ACTPM |
| Unexpected reading at N terminal | Neutral trace, harness or PCB connection issue | Inspect main PCB and wiring |
5. Common failure symptoms
- Breaker or power-supply circuit trips immediately at startup.
- DC bus voltage is unstable and the compressor does not start.
- Fuses repeatedly fail due to a DC-link short.
- PFC, active-filter or DC-voltage error is displayed.
- Power PCB fault indication appears immediately after energising.
6. Additional diagnostic checks
- Confirm the main power PCB is not shorted before replacing the ACTPM.
- Inspect the surge suppressor, rectifier, fuse circuit and associated harnesses after an ACTPM short.
- Cross-check inconsistent readings against a known serviceable module of the same part number.
- Do not interchange modules with different rated voltages, including 240 V and 415 V variants.
7. Reference images
Summary: Test only with power isolated and capacitors discharged. Normal readings are generally in the hundreds-of-kilo-ohms range, except for the designated neutral reference. Abnormally low, shorted or open readings indicate an internal ACTPM fault or an associated PCB/wiring issue.