Danfoss FC302 AL-98 Fault — What It Means
The AL-98 fault (often displayed as Warning 98) on a Danfoss FC302 VFD indicates a Clock Fault. The internal Real-Time Clock (RTC) chip has not been set, has failed, or the stored time data has been lost. This is typically a warning rather than a trip, so the drive can usually continue operating, but time-based functions like scheduling, data logging with timestamps, or automatic start and stop routines will be unreliable or inactive.
The fault is usually triggered by a power interruption combined with a failing backup circuit that cannot sustain the RTC, or by a hardware failure of the RTC integrated circuit on the control board itself. It is distinct from internal hardware faults and specifically points to the clock subsystem.
Before You Replace Anything
Technicians sometimes replace the entire power board when the fault is actually on the control PCB. Test by swapping the logic card first, which is a faster and cheaper diagnostic step.
Common Causes
- Power interruption with backup failure (~45%) A loss of mains power combined with a failing DC-link backup capacitor or control supply circuit that cannot sustain the RTC microchip during shutdown.
- Control board RTC IC failure (~30%) The Real-Time Clock integrated circuit on the control PCB has physically failed or is damaged.
- Firmware or software glitch (~15%) Corrupted firmware or a reset in the logic card causing the clock to default to zero or an invalid state.
- Environmental stress on control board (~10%) Excessive heat or vibration has damaged components on the control board, including the RTC circuit.
Quick Diagnosis
Answer these to narrow it down fast.
Does the warning clear when you press the Reset key on the LCP?
No: The warning is latched and likely indicates a hardware failure on the control board. Proceed with power cycle and board inspection.
Does the warning return immediately after a full power cycle (AC mains off for 10 minutes)?
No: The fault may have been a one-time event from a power glitch. Set the clock parameters and monitor the drive for several days.
Is the internal 10 V control supply stable and within 9.5 V to 10.5 V?
No: An unstable control supply can cause RTC and other logic faults. The control board or power board may need replacement.
Step-by-Step Fix
- Clear the warning by pressing the Reset key on the Local Control Panel (LCP) and observe whether it returns immediately.
- Set the clock manually using the drive parameters in Group 14 or the specific RTC parameter group to verify that the RTC can accept new data.
- Perform a full power cycle by disconnecting AC mains and any remote DC-link power (including UPS or batteries), then wait 5 to 10 minutes for the DC link to discharge completely before reconnecting power.
- Inspect the control PCB for visible damage such as burnt components, cracked integrated circuits, or signs of overheating on the logic card.
- Test the internal control supply by measuring the 10 V rail with a multimeter. Voltage should be between 9.5 V and 10.5 V under normal operation.
- Swap the control PCB (logic card) with a known-good unit to confirm whether the RTC fault is isolated to the control board.
- Monitor the drive after repair for several operating cycles to make sure the clock retains settings and the warning does not recur.
Parts Often Needed
| Part | Notes |
|---|---|
| Danfoss FC302 Control PCB (Logic Card) | Amazon | The standard replacement for RTC and clock faults. Confirm voltage rating and frame size match your drive model. |
| Danfoss FC302 Power Board | Amazon | Only needed if the 10 V control supply is unstable or damaged, which can affect the RTC circuit. |
When to Call a Pro
Call a qualified technician or control systems integrator if you are not comfortable working inside the VFD enclosure or handling control board diagnostics. This fault involves electronic troubleshooting and board-level repair, which requires familiarity with VFD internals, safe lockout and tagout procedures, and access to replacement control boards. If the drive is still under warranty or part of a critical industrial process, professional service is recommended to avoid downtime and make sure proper documentation of the repair.
Rough cost: A pro service call runs about $300-800 depending on control board replacement and labor.