Error Code 1500

If your Mitsubishi City Multi system is showing error code 1500, there is too much refrigerant in the system.

That surprises most building managers, who reasonably expect refrigerant faults to mean a shortage. Overcharge is the opposite problem, and it is almost always something that was done to the system rather than something that failed.

What this means for your building

Every VRF system is designed for a specific refrigerant charge. Too little and it cannot carry heat properly. Too much and pressures rise beyond where the system was designed to operate.

Error 1500 reports that the charge is above what the design calls for.

Because refrigerant does not appear on its own, this means somebody added it — and that is the thread worth pulling.

The preliminary code

1600 is the preliminary code for 1500. It appears when overcharge is detected but not yet confirmed.

A 1600 sitting in your fault history means the condition was developing before it became a lockout. Acting on preliminary codes is consistently cheaper than acting after them, and almost nobody looks.

Where overcharge comes from

Nearly always previous service work:

• A top-up instead of a leak repair. The system lost charge, someone added more, and the leak was never found. Repeat that a few times and the system carries too much.
• Charge added by estimate rather than weight. Correct charging is weighed to specification, not judged.
• A recharge without full recovery of what was already in the system.
• Charge added to mask a different fault, such as poor performance caused by airflow or a restriction.

That first one is the pattern we see most, and it carries an uncomfortable implication: if your system was topped up repeatedly, you may have both an overcharge and an unrepaired leak. Those coexist more often than people expect.

How urgent is it?

Urgent, though not dramatic.

Nothing is escaping and nothing is at safety risk. But an overcharged system operates at elevated pressure whenever it runs, which means the compressor is working harder than designed — every hour, not just on hot days.

There is a second risk. Excess refrigerant can result in liquid returning to the compressor rather than vapour. Compressors compress vapour; liquid causes mechanical damage.

What it typically costs

Moderate.

Recovering excess refrigerant and correcting the charge properly is a contained job — recovery, weighing, and recharging to specification.

The variable is what else is found. If the overcharge was masking a leak, that becomes a leak repair as well. If it was masking a different performance problem, that needs addressing too.

Set against the compressor wear that continuous high-pressure operation causes, correcting it promptly is straightforwardly the cheaper path.

What happens if you leave it

The compressor pays.

Sustained elevated pressure accelerates wear in a way that does not show up until it does. And if liquid is returning to the compressor, the damage is mechanical and cumulative.

There is also a diagnostic cost. An overcharged system produces misleading readings. A technician diagnosing an unrelated fault has to work around a system that is not operating at design conditions, which makes everything else harder to interpret.

What we check

1. Verify the charge against system design rather than assuming the code is right.
2. Recover excess refrigerant properly rather than venting or estimating.
3. Recharge to specification by weight.
4. Check for a leak — if repeated top-ups caused the overcharge, the original leak is likely still present.
5. Measure system pressures before and after to confirm the correction.
6. Review service history — prior charging work is nearly always the origin.
7. Check for related faults such as high pressure or discharge temperature codes that overcharge may have triggered.

What you can tell us before we arrive

• Has refrigerant been added, and how often? The single most useful thing you can tell us.
• When was the system last serviced? Overcharge is introduced during work, so timing points directly at it.
• Do you have service records? Even partial ones help establish what was added and when.
• Any other codes appearing? High pressure and discharge temperature faults often accompany overcharge.

Related codes

• 1302 — High pressure fault. Overcharge is a recognised cause.
• 1102 — Discharge temperature fault. Can accompany the elevated operating conditions overcharge creates.
• 4240 — Overload protection. The compressor working harder against higher pressure.

Get the charge corrected and the cause found

We are certified on Mitsubishi, Daikin and LG VRF platforms, and we service systems we did not install — including sorting out what previous contractors added to them.

Next business day service for commercial VRF.