What actually happens on an air conditioning installation day

Updated September 6, 2026 · Claude AC · 2 sources cited

The unit is chosen, the quote is signed, and a date is in the diary. Almost nobody explains what that day looks like, which is a shame, because an air conditioning installation is one of the rare purchases where the quality of the work is more consequential than the brand on the box — and where a homeowner standing quietly in the corridor can see most of the evidence for themselves.

Before the fitters arrive

Everything below assumes the preparatory decisions were settled at survey, not improvised on the morning.

• Positions agreed in writing. Indoor unit height and wall, outdoor unit location, the exact route of the pipes, and where they emerge on the façade. This is the single most common source of same-day arguments.
• Permissions in hand. Freeholder, co-owners, listed-building or planning consent where it applies — the map is in our guide to who has to say yes before you install air conditioning in Europe.
• The electrical side settled. Whether the job includes a dedicated circuit, who runs it, and whether your contracted power copes; the detail sits in our guide to the electrical side of an air conditioner.
• Access. Ladder or tower for the outdoor unit, parking for the van, a lift booking in an apartment block, and neighbours warned about an hour of core drilling.
• The room cleared. Two to three metres of clear floor under the indoor position, furniture moved, fragile things elsewhere. Core drilling makes dust regardless of how careful anyone is.

The day, step by step

1. Marking out. Indoor bracket levelled and fixed, positions checked against the agreed layout, wall scanned for cables and pipework before anything turns.
2. The core drill. A hole of roughly 55 to 80 mm depending on the manufacturer, bored with a slight fall towards the outside so condensate can never track back in. Wet drilling means water; dry drilling means dust; both are normal.
3. Indoor unit hung and the pipe tail dressed through the wall — refrigerant lines, condensate hose and interconnecting cable, each pipe insulated separately rather than wrapped as a bundle.
4. Outdoor unit set on wall brackets or floor feet, level, with anti-vibration mounts and the clearances the manual specifies around the coil and the fan discharge.
5. Pipework connected, flares cut and formed cleanly and tightened to the torque figure in the manual, or press-fitted where the system uses that method.
6. Strength test with dry nitrogen. The pipework is pressurised and left to sit while the fitters do something else, so a leak reveals itself before any refrigerant is released.
7. Evacuation. A vacuum pump pulls the system down and a gauge holds it there, then the pump is isolated and the reading is watched for decay. This is the step to watch.
8. The charge released from the outdoor unit, plus additional refrigerant weighed in if the pipe run exceeds the pre-charged length.
9. Electrical connection and condensate route completed — falling to a drain by gravity wherever possible, or through a condensate pump where the geometry gives no fall.
10. Commissioning. The system runs in cooling, and the fitter records readings: supply and return air temperatures, running current, pressures where accessible. Then the handover.

The two steps that decide the next fifteen years

Steps 6 to 8 are where good and bad installations separate, and both are invisible in the finished job.

Evacuation removes air and moisture from the pipework. Moisture left inside circulates with the oil, reacts under compressor heat, and produces the acid that quietly degrades windings and blocks expansion devices years later. It is also the step most easily faked: a pump run for five minutes looks identical, from the corridor, to a pump run properly with a decay test at the end. Ask to see the gauge and how long it held. A professional will show you without hesitation.

The charge is the second. Manufacturers pre-charge the outdoor unit for a pipe run of a few metres — commonly around five to seven, with the exact figure and the grams-per-extra-metre printed in the installation manual — and anything longer needs refrigerant weighed in on scales. Both directions hurt: undercharged systems lose capacity and run the compressor hot, overcharged ones raise head pressure and consume more for the same cooling. Field studies of installed systems repeatedly find incorrect charge among the most common causes of underperformance, which is why a machine rated at a high seasonal efficiency can behave like a mediocre one from day one.

How long it takes

Durations are indicative and assume the electrical supply is ready. Where a new dedicated circuit has to be run from the consumer unit, expect an extra half-day and, in several countries, a separate qualified trade. Costs for each of these shapes of job are broken down in our guide to what it costs to install air conditioning in Europe.

Signs of a rushed installation

• No nitrogen cylinder and no vacuum pump anywhere in the van.
• Gauges never connected, or connected for a couple of minutes only.
• The condensate pipe running uphill for part of its route, or discharging where the water will stain the façade or fall on a neighbour’s balcony.
• Refrigerant pipe insulation stopped short outside, or the two lines wrapped together inside one sleeve.
• Bare pipes and cable pinned across a façade with no trunking, on a building where that will cause you trouble later.
• No commissioning readings offered, and no paperwork beyond an invoice.

What you should hold at the end

Ask for the commissioning readings in writing, the installer’s refrigerant-handling certification details, the manufacturer’s warranty registration, the manuals for both units and the handsets, and a photograph of the condensate route before any boxing-in goes over it. That photograph costs nothing on the day and saves a diagnostic hour the first time water appears. Handling refrigerants is a certified activity across the EU under the F-gas rules, so the certification detail is not a formality — it is the evidence that the person who charged your system was entitled to.

Frequently asked questions

How long does it take to install one air conditioner?

A straightforward single split, with the outdoor unit on the other side of the same wall and an electrical supply already in place, is typically a half-day job for a two-person team. Longer pipe runs, a condensate pump, difficult access or a multi-split push it to a full day or several. Any quote promising three units in a morning is quoting an installation with steps missing.

Do I need to be at home for the whole installation?

You need to be there at the start, to confirm positions before anything is drilled, and at the end for the handover and the commissioning readings. The middle hours are noise and dust. If you cannot be present throughout, be present for those two moments — they are the ones where your decisions and your evidence matter.

How much mess does it make?

The core drill is the messy step, and it is over in under an hour. Wet drilling produces slurry that has to be caught; dry drilling produces fine dust that travels further than anyone expects. Clear the room, close the door to the rest of the flat, and expect the fitters to sheet the floor. Everything after the drilling is clean work.

Can air conditioning be installed in winter?

Yes, and it is often the better time — installers are far less busy outside the cooling season, and a reversible unit commissioned in the cold can be tested in heating mode immediately. The only real constraint is that cooling-mode commissioning is hard to verify meaningfully when it is a few degrees outside, so ask how the system will be proven and arrange a check the following spring if there is any doubt.

Can the outdoor unit go on a balcony or behind shutters?

Often yes, but not anywhere. The unit needs unobstructed air onto the coil and a clear discharge path, so an enclosure with a solid front recirculates its own hot air and the machine loses capacity precisely on the hottest day. Louvred screens sized to the manufacturer’s free-area figure are the usual compromise, and in an apartment block the balcony position is also a legal question before it is a technical one.

Read next

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• Europe’s heatwaves: the record of a continent warming fastest
• Why your air conditioner smells, and how to clear it for good
• When to buy air conditioning in Europe: the calendar that sets the price
• Air conditioning in a bedroom: cooling designed around sleep

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