Danfoss FC302 AL-93 — What It Means
No fault code named AL-93 exists in Danfoss FC302 VFD documentation. The FC302 series has over 90 documented alarms, but AL-93 is not among them. This code is either misread from the display, a typo in logging, or belongs to a different drive manufacturer (Yaskawa, Mitsubishi, or others use different numbering). The most common Danfoss FC302 faults that may be confused include AL-13 (overcurrent, triggered when output current exceeds 150-160% of rated current), AL-14 (earth fault), AL-29 (overtemperature), and AL-38 (internal fault with extended code in parameter 15-32).
If you see AL-13, it typically means mechanical overload, incorrect motor parameters, motor winding shorts, or failed IGBT modules. If you see AL-38, the drive has detected an internal hardware or sensor fault and will display a sub-code in parameter 15-32. Always verify the exact code on the drive display and consult the FC302 operating manual alarm table before ordering parts or attempting repairs.
Before You Replace Anything
Technicians sometimes replace the entire power board when AL-13 appears, but a simple megohm test of motor windings (should read above 2 MΩ to ground) or disconnecting the motor can reveal whether the fault is in the drive or the load.
Common Causes
- Misread or transcription error (~60%) The technician or operator recorded AL-93 instead of AL-13, AL-38, or another valid code from a poorly lit display or handwritten log.
- Wrong drive model or brand (~25%) The drive is not a Danfoss FC302, or a third-party control board with non-standard firmware is installed.
- Custom or modified firmware (~10%) A non-original control board or aftermarket parameter set is generating an unsupported alarm number.
- Display or control board corruption (~5%) The control board has corrupted memory or a failing display that shows garbled digits.
Quick Diagnosis
Answer these to narrow it down fast.
Does the drive display show AL-93 clearly, or could it be AL-13 or AL-38?
No: Re-read the code carefully. AL-13 (overcurrent) and AL-38 (internal fault) are the most common FC302 alarms and require different diagnostic paths.
Does the alarm appear only when the motor is running under load?
No: The fault is likely internal to the drive (AL-38 internal fault, failed gate driver, control board, or sensor). Check parameter 15-32 for the extended fault code and replace the identified component.
Can you access parameter 15-32 to read an extended alarm code?
No: Cycle power and attempt to enter the parameter menu. If the drive remains locked or unresponsive, the control board or display may be failed and requires replacement.
Step-by-Step Fix
- Verify the exact alarm code on the drive front panel display. Take a clear photograph if possible and compare it to the FC302 alarm list in the operating manual.
- Check the drive nameplate to confirm the model is FC302 and not a different Danfoss series (FC301, FC51, VLT Micro) or another manufacturer’s VFD.
- Access parameter 15-32 using the keypad or PC software to read the extended alarm code if the display shows AL-38 (internal fault).
- Disconnect the motor from the drive output terminals U, V, W and attempt to run the drive unloaded. If the alarm clears, the fault is motor or mechanical. If it persists, the drive has an internal fault.
- Perform a megohm test on the motor windings from each phase to ground and phase to phase. Readings below 2 MΩ indicate insulation failure and motor replacement is required.
- Inspect input power for voltage imbalance (should be within 3 percent across phases) and loose connections at the drive input terminals L1, L2, L3.
- Replace the identified failed component (control board if AL-38 with a sensor or logic fault, power board or IGBT modules if AL-13 persists with motor disconnected, or motor if winding insulation is compromised).
Parts Often Needed
| Part | Notes |
|---|---|
| FC302 control board (logic PCB) | Amazon | Required if AL-38 internal fault points to a failed sensor, gate driver, or corrupted parameter memory. Match the drive frame size and firmware version. |
| FC302 power board (rectifier and inverter assembly) | Amazon | Required if AL-13 overcurrent persists with the motor disconnected, indicating failed IGBT modules or DC link capacitors. |
| IGBT module (per phase) | Amazon | Can be replaced individually if the power board is modular and only one phase is shorted. Must match drive voltage and current rating. |
| Three-phase motor | Amazon | Required if megohm test shows winding insulation below 2 MΩ or phase-to-phase shorts. Must match nameplate specs in parameters 1-20 through 1-25. |
When to Call a Pro
Call a qualified VFD technician or industrial electrician whenever the drive displays any alarm code. Diagnosis requires safe isolation of high-voltage DC bus capacitors (which can hold lethal charge for minutes after power-off), multimeter testing of IGBT gate signals, and parameter programming. If the alarm is truly AL-93 and not a misread, the drive may have third-party firmware or be a counterfeit unit, and a Danfoss-certified service partner should inspect it. Do not attempt to open the drive enclosure or measure internal voltages without proper training, insulated tools, and lockout/tagout procedures.
Rough cost: A pro service call runs about $300-800 depending on whether the fault is motor-side or drive internal.