What happens on installation day

A wall-mounted split is usually fitted in much the same order. Some stages are loud and quick, and others are long, quiet waits while gauges are read. Knowing the sequence helps you plan your day and recognise careful work when you see it.

The day at a glance

A straightforward single-room installation often takes from half a day to a full day. Longer pipe routes, more rooms or electrical work at the consumer unit can add time, and the order of the stages can vary a little between installers.

Getting started

The work is usually done by one or two engineers. A good installer starts by walking through the job with you: the exact spot for the indoor unit, where the pipes leave the room, where the outdoor unit sits and where the water will drain.

Dust sheets go down and the wall is checked for hidden cables and pipes before any drilling. If something differs from the survey, such as a pipe where the hole was planned, this is the moment positions get adjusted. It helps to have rooms and access cleared beforehand, as covered in preparing your home for installation.

You don't need to watch, but be around at the start to agree positions and at the end for the handover.

Fitting the indoor unit

A metal mounting plate is screwed to the wall and checked with a spirit level. The indoor unit later hangs on it.

Next comes the hole for the pipes. A diamond core drill cuts a neat circle through the wall, roughly the width of a drinks can, often with a vacuum held at the bit to catch dust. The hole slopes slightly down towards the outside so rain can't run in and the drain water can run out. This is usually the loudest part of the day, but it typically lasts minutes rather than hours.

The refrigerant pipes, drain hose and connecting cable are taped into one bundle, with the drain hose at the bottom so water flows freely, and fed through the wall, often inside a plastic sleeve. The unit then hangs on its plate.

Fitting the outdoor unit and pipes

Outside, the outdoor unit goes on wall brackets or a ground stand, sitting on rubber anti-vibration mounts and set level.

The copper pipes are cut to length, bent smoothly without kinks and insulated along their whole length. At the units, the pipe ends are shaped with a flaring tool and tightened with a torque wrench to the manufacturer's setting. Any joints that are brazed instead are made with nitrogen flowing through the pipe, which stops scale forming inside. The details are in refrigerant pipework explained.

Along the outside wall the pipes usually run in plastic covers that protect the insulation from sunlight and knocks. The drain hose is given a steady fall to a suitable outlet, or connected to a small pump where gravity can't do the job.

Testing the refrigerant circuit

At this point the refrigerant is still sealed inside the outdoor unit, behind closed valves. Before it's released, the new pipework has to be proved sound and clean.

• Pressure test. The pipes and indoor unit are filled with dry nitrogen at high pressure and left for a period. A drop on the gauge points to a leak, and joints are checked with leak-detection spray. Nitrogen is used because it's dry and doesn't react, and since air is mostly nitrogen, letting it out afterwards does no harm.
• Vacuum. A vacuum pump draws out the air and moisture left inside. A gauge shows when the vacuum is deep enough, then the pump is isolated to check it holds. Air and moisture left in the circuit reduce performance and can damage the system over time.
• Releasing the charge. The engineer opens the valves on the outdoor unit and the refrigerant flows into the pipes and indoor unit. If the pipe run is longer than the factory charge allows for, extra refrigerant is weighed in from a cylinder.

These steps can't be hurried. Long, quiet stretches with a vacuum pump humming are a normal part of the job.

Power, testing and handover

Most systems need their own circuit from the consumer unit, so your electricity is usually switched off for a while during the connection. An isolator switch is often fitted near the outdoor unit. The work may be done by the air conditioning engineer or by a separate electrician, as explained in electrical requirements.

With the power on, the system is run in cooling and heating to check that it cools and heats properly and runs without unusual noise or vibration. Water is poured into the indoor unit's drip tray to prove the drain works.

Finally, the gap around the pipes is sealed inside and out, and the work area is cleaned. You should be shown how to use the controls and clean the filters, and given the paperwork: the commissioning record, the electrical certificate and a copy of the noise calculation for the outdoor unit. What each document is for is covered in commissioning and handover.