Error Code 1301

If your Mitsubishi City Multi system is showing error code 1301, low-side pressure dropped below its safe threshold and the system stopped.

On a commercial VRF system, this is the code we most want to catch early — because the most common cause is a refrigerant leak, and leaks get more expensive the longer they run.

What this means for your building

The low pressure sensor watches the suction side of the refrigerant circuit. When pressure falls below the safe operating range, the system shuts down rather than run in a condition that damages the compressor.

Pressure falls for a small number of reasons, and they differ enormously in cost:

• There is less refrigerant in the system than there should be — it leaked out
• Refrigerant cannot flow properly — a restriction, a failed expansion valve, a blocked filter
• The sensor is reporting incorrectly — the cheapest outcome, and worth ruling out

How urgent is it?

Urgent, and the urgency is financial.

If the cause is a leak, refrigerant is escaping right now. The amount lost directly drives what the repair costs, because recharging a commercial VRF system is not a small line item. Every day of delay is more refrigerant gone.

There is also equipment risk. Refrigerant carries oil through the system and helps cool the compressor. Running low means running hot and under-lubricated.

What it typically costs

Medium to high, and this code has one of the widest ranges on the list.

A faulty sensor is a modest repair. A restriction or failed expansion valve is moderate. A leak is the expensive scenario, and on VRF specifically it is expensive in a way that surprises building owners.

Commercial VRF systems hold a large refrigerant charge distributed across long pipe runs with many joints and branch connections. Finding the leak means systematically isolating and testing sections. Then the remaining charge has to be recovered properly, the repair made, the system pressure tested, evacuated, and recharged.

The refrigerant itself is a genuine cost at that volume, and the labour to do it correctly is substantial.

Why “just top it up” is not a repair

This comes up on nearly every low-charge call, so it is worth being direct.

Refrigerant is not consumed. It does not wear out or get used up. If the level dropped, it went somewhere — which means there is a leak, and it is still there after you top up.

Adding refrigerant without finding the leak means:

• Paying for refrigerant again, on a schedule that gets shorter
• Releasing refrigerant to atmosphere, which carries regulatory weight at commercial charge volumes
• Leaving a leak to grow, because they rarely stay the same size

We will tell you plainly if a top-up is a reasonable stopgap while a repair is scheduled. We will not sell it as a fix.

What causes it

• Refrigerant leak — the most common, and the one that drives cost
• Failed or stuck expansion valve restricting flow
• Blocked filter or drier creating a restriction
• Faulty low pressure sensor reporting a drop that is not real
• Undercharge from a previous service where the system was never properly filled

What happens if you leave it

Two things get worse in parallel.

The leak grows. Joints and connections that have started to fail rarely stabilise. More refrigerant escapes, and the eventual recharge costs more.

The compressor wears. Running a system low on charge means poor oil return and inadequate cooling. Compressor replacement is the most expensive repair on a VRF system, and low-charge operation is one of the most common paths to it.

A leak found early is a repair. The same leak ignored is a repair plus a compressor.

What we check

1. Confirm the pressure reading is real — verify the sensor before assuming a charge problem.
2. Assess the actual refrigerant charge against system design.
3. Leak detection across the circuit, isolating sections on long runs to narrow the location.
4. Inspect likely failure points — joints, branch connections, valve bodies, and areas exposed to vibration.
5. Check the expansion valves for correct operation, since a restriction imitates a leak on the gauges.
6. Inspect filters and driers for blockage.
7. Review service history — a system that has been topped up before almost certainly has a leak that was never found.

What you can tell us before we arrive

• Has refrigerant been added before? This is the single most useful thing you can tell us. Prior top-ups mean a known, unrepaired leak.
• When did performance start dropping? Systems usually lose capacity gradually before the code appears.
• Has any work been done on the pipework? Tenant improvements, ceiling work, or anything that disturbed refrigerant lines.

Related codes

• 1302 — High pressure fault. The opposite condition, generally pointing at heat rejection problems.
• 1102 — Discharge temperature fault. Low charge frequently drives discharge temperature up, so these often appear together.

Get the leak found, not just the charge topped up

We are certified on Mitsubishi, Daikin and LG VRF platforms, and we service systems we did not install.

Next business day service for commercial VRF.