What does Danfoss FC302 Alarm 38 - Causes & Fix mean?

Danfoss FC302 Alarm 38 means internal fault, usually a communication error between control and power cards. Reset steps inside.

How do I fix Danfoss FC302 Alarm 38 - Causes & Fix?

Follow the step-by-step diagnosis below. The most likely fix is identified by checking power, sensor resistance, and control-board signals in order — using a multimeter and the part numbers documented in the parts reference table.

Can I keep running the equipment with FC302 active?

Generally no. Faults on Vfd units are emitted when a sensor, safety, or control circuit is outside its operating envelope. Running through an active fault risks compressor, heater, or control-board damage. Diagnose and clear the fault first.

What part is most commonly replaced for Danfoss FC302 Alarm 38 - Causes & Fix?

The most frequently replaced parts for Danfoss FC302 Alarm 38 - Causes & Fix are listed in the Parts Reference section of this guide with OEM part numbers and typical price ranges. Check the table for direct replacements.

Is Danfoss FC302 Alarm 38 - Causes & Fix a DIY repair or do I need a technician?

Sensor swaps, fan motor replacements, and condenser cleaning are typical DIY-level repairs. Anything involving refrigerant, gas, or high-voltage (>240V) work requires a licensed technician for both safety and code-compliance reasons.

Danfoss FC302 Alarm 38 - Causes & Fix

Danfoss FC302 Alarm 38 — What It Means

Alarm 38 on the Danfoss VLT FC302 indicates an internal fault. This is not a single field-replaceable failure but a broad category that requires further diagnosis. The drive will display a subcode to help narrow down the problem. According to Danfoss technical support, the most common cause of Alarm 38 is a communication error between the control card and the power card inside the drive. The fault can appear after a disturbance, maintenance work, or component failure that interrupts the internal signal path between these boards.

Jump to Fix

Common Causes

Communication failure between control card and power card This is the specific internal fault Danfoss identifies for Alarm 38 in its support documentation.
Loose or disconnected internal connectors Vibration, maintenance, or installation errors can unseat the ribbon cables or connectors linking the control and power boards.
Failed control card Electronic component failure on the control card can stop it from communicating with the power section.
Failed power card A fault on the power card can prevent it from responding to control signals or reporting status back to the control board.
Improperly seated or incompatible option card If an option card is installed, poor contact or board-level incompatibility after a replacement can trigger internal fault alarms.
Electrical surge or disturbance Transient voltage events can damage internal electronics and disrupt board-to-board communication paths.

Step-by-Step Fix

Cycle power by switching off the drive, waiting 30 seconds, and powering it back on to attempt a reset as Danfoss recommends.
Note the displayed subcode or any additional numbers shown with Alarm 38 and write them down for reference.
Power down completely and lock out the drive, then open the enclosure to access the internal boards.
Inspect and reseat all internal connections, paying special attention to the ribbon cables and connectors between the control card and power card, and check that any installed option cards are firmly seated.
Look for physical damage such as burn marks, corrosion, or loose solder joints on the control card, power card, and interconnects.
Power up and test the drive after reseating connections to see if the fault clears.
Contact Danfoss technical support with your drive model, serial number, and subcode if the alarm persists, because the exact internal fault code determines which board requires replacement.

Parts Often Needed

Part	Notes
Danfoss FC302 Control Card	Amazon \| Required if diagnostics or Danfoss support confirm control-side communication failure.
Danfoss FC302 Power Card	Amazon \| Needed when the power section is not responding to the control board.
Internal Ribbon Cable or Connector Kit	Amazon \| Use if visual inspection shows damaged or broken interconnects between boards.

When to Call a Pro

Call a qualified VFD technician or contact Danfoss technical support if cycling power and reseating internal connections does not clear Alarm 38. Internal board diagnosis requires knowledge of the specific subcode, access to internal schematics, and safe handling of live power electronics. If you are not trained to open and service the drive or lack the tools to isolate board-level faults, professional repair or factory service is the safest route. Danfoss support can guide board replacement based on the exact fault code displayed.