VFD Troubleshooting Checklist: 10 Things to Check Before Calling Support

Before you call the drive manufacturer's support line and spend 45 minutes on hold, run through this checklist. Eight out of ten VFD faults can be resolved with these checks — and you'll look like a hero for getting the line back up in minutes instead of hours.

The 10-Point VFD Checklist

1. Read and record the fault code. Check the fault history for patterns — is it the same fault repeating, or different faults? Write it down before clearing.
2. Check input power. Measure L1-L2, L2-L3, L1-L3 at the drive terminals. All three should be within ±10% of the drive's rated voltage and within 3% of each other.
3. Check the cooling fan. Is it spinning? Is there airflow out the top of the drive? A dead fan is the #1 cause of overtemperature faults.
4. Check the ambient temperature. Hold your hand inside the enclosure — if it's uncomfortable, it's too hot for the drive. Max is typically 40°C (104°F).
5. Inspect motor cables. Look for physical damage, especially at conduit entries and junction boxes. Damaged insulation causes overcurrent and ground fault trips.
6. Megger the motor. Disconnect motor cables from the drive. 500V DC, 60 seconds, phase-to-ground. Must be >1 MΩ. If it fails, the problem is the motor or cable, not the drive.
7. Check motor cable connections. Loose output terminals cause intermittent faults. Torque all terminals to spec.
8. Check the drive parameters. Was anything changed recently? Most drives have a "parameter change log" or you can compare against a saved parameter file.
9. Clear the fault and restart. If the fault returns immediately, the problem is still present. If it takes minutes/hours, suspect a thermal or intermittent issue.
10. Disconnect the motor and restart the drive. If it runs fault-free with no motor connected, the problem is in the motor or cables. If it still faults, the drive has an internal failure.

When to Call Support

Call the manufacturer when: the drive faults with no motor connected, the drive won't power up at all, the display is blank or showing garbled characters, or you've been through all 10 checks and the fault keeps recurring. Have the drive model number, serial number, firmware version, and fault history ready — this will cut your call time in half.