If your Mitsubishi City Multi system is showing error code 4250, the inverter detected current beyond safe limits and shut down.
This is the code family we treat most cautiously, because it spans everything from a recoverable board fault to a failed compressor — the single most expensive repair on a VRF system.
Read the detail code first
Before anything else: write down the number in brackets.
4250 is not one fault. It is six, and the detail code is what distinguishes them:
| Detail | What it indicates |
|---|---|
| 101 | IPM error — the power module protecting the inverter has faulted |
| 103 | DCCT overcurrent detected in hardware at the sensing circuit |
| 104 | Short-circuited IPM or ground fault |
| 105 | Overcurrent from a short-circuited motor — points at the compressor |
| 106 | Instantaneous overcurrent detected in software — a sudden spike |
| 107 | Overcurrent by effective value — sustained draw above limits |
The difference between 101 and 105 is roughly the difference between a board repair and a compressor replacement. That single number is the most valuable thing on your controller, and it is frequently lost because someone resets the fault before recording it.
What this means for your building
The inverter controls compressor speed by varying the power delivered to it. It monitors current continuously, because excessive current is how both inverters and compressors destroy themselves.
When current exceeds limits, the system stops immediately. That is not a graceful shutdown — it is a protective cut, and it happens fast because the alternative is component damage.
The preliminary code
4350 is the preliminary code for 4250. If it appears in your fault history, the system detected the condition before it became a lockout.
Preliminary codes in this family are worth taking seriously. A compressor developing a winding fault or an inverter with a degrading power module often signals before it fails outright.
How urgent is it?
Critical. This is the code where continuing to run the system is genuinely capable of turning one expensive repair into two.
If the underlying condition is a short circuit or ground fault, each restart drives fault current through components already compromised. A failed compressor can take a healthy inverter with it. An inverter with a failing power module can damage a healthy compressor.
No safety hazard to occupants, but real risk to equipment with every restart attempt.
What it typically costs
Highest. This is the top of the cost range for VRF faults.
At the lower end, an inverter board fault is a significant but bounded repair. At the upper end, a short-circuited compressor means the compressor itself, refrigerant recovery, system cleanup where contamination has occurred, and substantial labour to remove and replace a large component in a commercial setting.
There is also a scenario worth knowing about: when a compressor fails electrically, it can contaminate the refrigerant circuit. Cleaning that up properly adds materially to the job, and skipping it puts the replacement compressor at risk.
What causes it
- Compressor winding failure or short — the expensive scenario, typically detail code 105
- Inverter power module failure — detail codes 101 or 104
- Ground fault in the compressor or its wiring — detail code 104
- Current sensing circuit fault — detail code 103, sometimes the least expensive outcome
- Supply voltage problems stressing the inverter, often alongside bus voltage codes
- Mechanical compressor problems causing it to draw excessive current under load
What happens if you leave it
Unlike most codes, the risk here is not gradual degradation. It is acute.
Repeatedly restarting against a genuine overcurrent condition can cascade. The most costly outcome we see is a building that reset 4250 many times over a weekend to keep tenants comfortable, and converted a compressor failure into a compressor and inverter failure.
If you are seeing 4250, the correct action is to leave the system off and get it diagnosed.
What we check
- Record the detail code — this drives everything that follows.
- Electrical testing on the compressor — winding resistance and insulation, to establish whether the compressor is the fault.
- Test for ground faults in the compressor and its wiring.
- Inspect the inverter board and power module for visible failure and test operation.
- Verify current sensing circuits — occasionally the fault is in measurement rather than current.
- Check supply voltage quality, since supply problems present as inverter faults.
- Assess refrigerant contamination if the compressor has failed electrically, because that changes the scope of the repair.
What you can tell us before we arrive
- The detail code in brackets. If nothing else, this one. Photograph the controller before resetting.
- How many times has it been restarted? This genuinely changes what we expect to find.
- Was there a supply issue? Outage, surge, or known voltage problems in the building.
- Any noise from the outdoor unit before it stopped? Mechanical compressor problems often announce themselves.
Related codes
- 4220 — Bus voltage abnormality. Supply-side problems that can present alongside inverter faults.
- 4240 — Overload protection. Sustained high load rather than acute overcurrent.
Do not restart it. Get it diagnosed.
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Related codes
Error 4220 covers inverter DC bus voltage faults. The detail code tells you whether the problem is your building's power supply or the inverter itself.
Error 4240 is overload protection. The compressor circuit drew high current too long — usually fighting a condition it could not overcome.
Frequently asked questions
What does error code 4250 mean on a Mitsubishi City Multi system?
It is an overcurrent fault on the inverter. Current drawn by the compressor circuit exceeded safe limits and the system shut down. It covers several distinct conditions, and the detail code shown alongside it identifies which one you actually have.
Why does 4250 come with a number in brackets?
That is the detail code, and it is the most useful information on your controller. It distinguishes an inverter power module fault from a short-circuited compressor motor. Those are very different repairs at very different costs, so record it before resetting anything.
Is error 4250 a failed compressor?
Sometimes. Detail code 105 indicates overcurrent from a short-circuited motor, which points at the compressor itself. Other detail codes point at the inverter board or its sensing circuits. Diagnosis must establish which, because guessing wrong is expensive in both directions.
How much does a 4250 error cost to repair?
This is potentially the most expensive fault on a VRF system. Board-level faults are moderate by comparison. A short-circuited compressor is the highest-cost repair there is, involving the component itself plus refrigerant recovery, system cleanup where contamination occurred, and significant labour in a commercial setting.
Can I keep resetting a 4250 error?
No, and this is the code where that matters most. If the underlying condition is a genuine short or ground fault, repeated restarts drive fault current through components that are already compromised, and can take a healthy inverter down along with a failed compressor.
What is the difference between 4250 and 4240?
Both are current-related, but 4240 is overload protection responding to sustained high load over time, while 4250 is overcurrent covering acute faults including short circuits and power module failures. 4250 generally indicates something electrically broken rather than a system simply working too hard.