Description
The Active Filter Module (ACTPM), also referred to as the Active PFC / IPM Module, is responsible for maintaining efficient power factor correction, ensuring smooth DC bus voltage regulation, and reducing harmonic distortion in the inverter drive circuit.
A failure within this component can result in power-on trips, fuse failures, or PCB damage due to excessive current draw.
This test verifies the ACTPM’s internal circuit integrity using resistance measurements under power-off conditions.
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 between the DC link (+ and – terminals) and manages charge/discharge timing.
| 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 |
| N1 (Blue) | Neutral output | DC side control link |
| P (Yellow) | DC positive output | Filtered DC voltage output |
2. Safety Precautions
⚠️ Before testing:
Ensure all power is OFF and the system has been isolated for at least 10 minutes to allow capacitors to discharge fully.
Disconnect all control and signal harnesses connected to the module to prevent back-feeding voltage.
Never perform continuity or megger testing on this module — only use resistance (kΩ) measurements.
3. Test Procedure – Resistance Check
Objective:
To confirm internal transistor and diode circuit integrity within the ACTPM under no-power conditions.
Instrument:
Digital Multimeter set to Auto-Range Resistance (kΩ)
Step 1 – Identify Terminals
Refer to the terminal labels on the ACTPM housing or schematic. Ensure clear access to (–, +, L1, L2, N, P).
Step 2 – Measure Resistance Values
| Multimeter Connection | Expected Resistance (kΩ) | Condition / Interpretation |
|---|---|---|
| Black (–) → Red (+) | 360 kΩ | Normal |
| Black (–) → L1 (White) | 360 kΩ | Normal |
| Black (–) → L2 (Brown) | >1 MΩ | Normal / High isolation |
| Black (–) → N (Blue) | 0 Ω | Common reference point |
| Red (+) → P (Yellow) | 720 kΩ – 900 kΩ | Normal range |
| N (Blue) → P (Yellow) | 360 kΩ – 540 kΩ | Normal range |
Step 3 – Evaluation
| Observation | Interpretation | Action Required |
|---|---|---|
| All readings within specification | ACTPM functioning normally | No action |
| 0 Ω between + and – | Short circuit (internal transistor failure) | Replace ACTPM |
| ∞ (Open circuit) between N and P | Open internal connection | Replace ACTPM |
| Low resistance across multiple terminals | Internal diode/transistor breakdown | Replace ACTPM |
| No continuity at N terminal | PCB communication or neutral trace fault | Inspect main PCB connection |
4. Common Symptoms of ACTPM Failure
| Symptom | Possible Cause | Effect |
|---|---|---|
| Power supply circuit trips immediately | ACTPM shorted internally | High inrush / breaker trip |
| DC bus voltage unstable | ACTPM control circuit fault | Inverter shutdown / compressor not starting |
| Fuses repeatedly blowing | DC link short through IPM | Replace ACTPM and inspect surge suppressor |
| Error code indicating “PFC / DC Error” | ACTPM voltage imbalance | Module malfunction or wiring issue |
5. Additional Diagnostic Notes
Always isolate and confirm the main power PCB is not shorted before replacing the ACTPM.
If readings are inconsistent between units, cross-check with a known working system.
An ACTPM short circuit will typically cause instant breaker trips or LED power board fault indication on startup.
Never interchange modules with differing rated voltage types (e.g., 240V vs 415V units).
6. Summary
Test only with power off.
Measure resistance values between designated terminals per the reference table.
Normal readings are in the hundreds of kΩ range, with 0 Ω only present at the neutral reference.
Deviations indicate transistor or diode failure within the ACTPM.
Always disconnect harnesses and verify PCB integrity prior to replacement.
