At 2:00 a.m., the last thing you want to see is a Danfoss VFD alarm in an HVAC mechanical room. Or maybe the drive's local control panel is completely dark, and the fan isn't running. You grab your phone and search for a danfoss vfd alarm list. The list gives you code definitions, but it doesn't tell you what to do next. That's the part people miss.
Here's why I can say that with a straight face: I've spent the last eight years coordinating emergency service calls for commercial and industrial electrical systems. A VFD alarm is never the whole story. It's a clue. The right next step depends on whether the drive has ever run, whether it used to run reliably, and whether other electrical devices in the building are also acting weird.
What Is a VFD in HVAC?
For anyone who landed here because of the keyword and not an emergency: a VFD is a variable frequency drive. It controls the speed of an AC motor by varying the voltage and frequency going to it. In an HVAC system, VFDs run supply fans, return fans, chilled water pumps, condenser fans, and cooling tower motors. Instead of running a pump or fan at full speed and adjusting flow with dampers or valves, a VFD just runs the motor slower. That's where the energy savings come from. The fan affinity law isn't a slogan, it's math: at 80% speed, a fan uses roughly half the energy it would at full speed.
Danfoss VFD drives are common in this space. The VLT HVAC Drive FC 102 is the model I see most often on commercial jobs. The same troubleshooting logic applies to the FC 202 and FC 302.
Danfoss VFD Alarm List: The Codes I Actually See
People ask me for the complete Danfoss VFD alarm list all the time. Honestly? That list belongs in the operating manual for your specific drive and firmware version. Danfoss has changed code numbers and names across drive generations. If someone quotes a code without verifying the model, don't trust it. As of January 2025, the VLT HVAC Drive FC 102 operating instructions still include the full alarm and warning table. Verify there before you replace anything.
That said, these are the alarms that show up in most emergency calls:
- Alarm 4, Mains phase loss. Check input fuses, the contactor, and the terminals. I've seen a loose lug cause a phase loss that only appeared when the motor was loaded.
- Alarm 7, DC overvoltage. Very common on fans and pumps. The motor is generating power back into the drive, often from windmilling or a deceleration time that's too short. The drive is not bad. The stopping strategy is wrong.
- Alarm 10, Motor overload. Check the motor nameplate and the actual current on each phase, then check bearings and the driven load.
- Alarm 14, Earth fault. Moisture in the motor cable is a top cause. Check junction boxes and long cable runs before you even think about a new drive.
- Alarm 16, Short circuit. Check the motor windings and the output cable. On rare days, the drive itself is bad.
That's not a universal list. It's a starting list. The code was never the useful part. The useful part is what the code means in your situation.
Three Scenarios, Three Different Moves
VFD troubleshooting is a decision tree. Different situations demand different moves. Here are the branches I use.
Scenario 1: The Drive Is New and Alarms Before the Motor Ever Runs
New Danfoss VFD drives don't fail often. New installations do. If the drive powers up, the keypad works, and then you get an alarm when you hit start, I look for installation mistakes first.
- Motor parameters copied from another drive or typed in wrong.
- A motor cable damaged during installation, or a junction box with condensation.
- A missing or floating ground.
- Phase imbalance on the incoming supply.
That last one can be sneaky. I once found the same loose neutral that was making an electrical socket not working on one floor was also dropping one phase to the VFD on another. The drive was trying to tell us the truth. Nobody believed it.
An earth fault alarm on a brand-new drive is not a mandate to replace the drive. It's a mandate to check the cable.
Scenario 2: The Drive Ran Fine for Months, Then Trips on a Schedule
When a drive has been running reliably and then develops a pattern, the drive is rarely the root cause. It's the device that's allowed to stop the motor. I know that's not what you want to hear at 2:00 a.m.
Check the trip log. Danfoss drives keep an event log, and the log gives you a pattern. Does the trip happen at startup? At the same time every afternoon? When a building automation command changes? A cooling tower fan that spins with the starter off can generate enough reverse energy to trip a DC overvoltage alarm. You can replace the drive, but the new drive will do the same thing the next day.
Earlier in my career, I cleared a repeated alarm on an FC 102, told the building engineer it was fixed, and got a callback four hours later. The engineer didn't mention the alarm code. He just said, "You're the second vendor who hasn't fixed this." That changed how I work. We now leave a voltage logger on site and capture current and DC bus events before quoting a repair. The logger costs less than one repeat visit. That's also why clients remember us as the people who actually found the problem.
Scenario 3: The VFD Alarm Is Not the Only Electrical Problem
This is the one that confuses everyone because the symptoms don't seem related. Two work orders land on your desk. One says "Danfoss VFD tripped on phase loss." Another says "control panel for Samsung stove stuck in reset loop." A third, if you're lucky, says "electrical socket not working in suite 302."
They're not three separate problems. A loose neutral can drop voltage on one phase across multiple circuits. The VFD sees phase loss. The stove control panel sees low voltage and reboots. The socket is dead because the shared neutral isn't actually shared anymore. One terminal screw, three work orders.
I remember this happening at a mixed-use building. The maintenance supervisor had to decide whether to bring me in for the VFD or send someone to the tenant's kitchen. I checked the feeder panel first. Tightened one neutral connection. Both issues disappeared. The alarm list had nothing to do with the stove. The voltage supply had everything to do with both.
How to Tell Which Scenario You're In
Here's the shortcut I use when I'm triaging a call:
- If the drive is new and never ran, treat it as an installation problem. Verify voltage, wiring, and motor parameters before you blame the drive.
- If the drive used to run and now trips repeatedly, log the events before you reset it again. The pattern is more useful than the code.
- If other electrical devices are acting up too, stop reading the alarm list and start testing the supply. Loose neutrals, phase imbalance, and ground faults love to wear costumes.
- If you're on the fence, check the incoming supply first. It's the cheapest thing to verify and the most common root cause.
Bottom Line: The Alarm Is Not the Diagnosis
People remember two things after a service call: whether you fixed it, and whether you made them feel confident. A Danfoss VFD alarm list can't do that for you. Verifying the context, checking the wiring, and fixing the root cause can.
In my role coordinating emergency service calls, I always tell clients the same thing: your Danfoss VFD drives are usually more reliable than the stuff connected to them. The alarm code is the first voice in the room. Actually, let me rephrase that: it's the loudest voice, not the diagnosis. Listen to it, but don't let it drown out the rest of the building.
Fix the root cause, not the code. The client will remember the difference.
