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Air assist isn't working on my laser

Machine & jobs · Updated: August 9, 2026

Air assist in Lùmen is a G-code command, nothing more: the app tells your controller to switch its coolant output on before the job's first move, and off at the end. Whether anything actually blows depends on your firmware and on how the pump is wired. When it doesn't work, the machine's answer tells you which of the two is at fault.

How it works, in one paragraph

Turn Air assist on in Machine settings (it's off by default) and pick a command pair: M8 / M9, the standard flood-coolant pair, or M7 / M9 for firmware built for mist coolant. From then on every job switches the pump with the laser — including jobs exported with Export G-code (offline) and run from the machine's SD card. There's also a manual Air button, and an Air On / Air Off indicator in the status strip. See the features page for the full behaviour.

1. The machine answers error:20

error:20 is GRBL for “unsupported command”. Your firmware doesn't implement that coolant command — the board isn't broken and the wiring isn't the problem yet.

• Try the other pair. In Machine settings switch from M8 / M9 to M7 / M9 (or the other way round) and press the Air button. M8 is compiled into every stock GRBL 1.1 build, but M7 only exists in firmware built with ENABLE_M7 — and some vendor firmware ships with neither.
• If both are rejected, the board has no coolant support compiled in. It cannot switch a pump under software control, whatever sender you use. Leave air assist off in Lùmen and run the pump from its own switch — and note that with air assist off, Lùmen emits exactly the G-code it always did.

Use the manual Air button for this test, not a real job: that's what it's there for. Finding out mid-cut that the board rejects the command is the expensive way to learn it.

2. Nothing happens, but there's no error

If the console shows no error, the controller accepted the command — so the suspect is downstream of the firmware:

• The pump must be on the controller's air-assist / coolant port. A pump plugged into a wall socket, a power strip, or a smart plug is invisible to the controller, and Lùmen only talks to the controller.
• Check the port is actually populated. On many diode machines the air-assist connector is present on the board but the pump kit is sold separately; some boards switch a low-current signal that drives a relay, and without that relay nothing moves.
• Listen at the board, not at the nozzle. A relay click with no airflow points at the pump or the tubing; no click at all points at the wiring.

Anything the controller can't switch, Lùmen can't switch either — there is no software workaround for a pump that isn't wired to the board.

3. Should I leave air assist on all the time?

If a pump is wired to the port: yes. Lùmen only runs it during jobs, so nothing is left blowing between cuts, and the airflow protects the lens as much as it improves the cut — smoke that doesn't leave the beam path settles on the optics.

Air assist is off by default for one reason only: Lùmen can't know whether your board supports the command, and a board that doesn't will say so in the middle of a job. Once you've verified it with the Air button, there's no reason to keep switching it off.

Two things Lùmen deliberately doesn't do

• Per-layer air. Air assist is global: on for the whole job, or off. If you need one operation dry and the next with air, Lùmen isn't the tool for that job today.
• Smart plugs and wall sockets. Only a pump wired to the controller's air-assist port can be switched. There's no network or Bluetooth control of external outlets.

Still stuck?

Reach out to support with your engraver model, the firmware it reports on connect, which command pair you tried, and what the console answered — those four lines are usually enough to tell a firmware limit from a wiring problem. For power, speed and material settings once the air is running, see the laser engraving settings chart.