Cleaning Your Air Conditioner Yourself Before Winter: The Real Protocol (and What to Leave to a Refrigeration Engineer)
L'équipe Proclimo
2 Oct 2026 - 08 min read
The smell always arrives at the same moment: the first week of October, you switch the split unit over to heating mode after four months of cooling, and the room smells like a cellar. It isn't that the machine has died — it's that the heat exchanger and the condensate tray spent the summer damp, at 25 °C, with organic dust sitting on them. In other words: a culture medium. And beyond the smell, there's the bill — a clogged indoor coil causes airflow to collapse, the COP falls apart, and the air-to-air heat pump compensates by drawing more current all winter long.
Autumn is the right window to deal with it. The cold hasn't settled in yet, the unit hasn't yet run in heating mode, and refrigeration engineers are less swamped than they are in June. Here's what you can safely do yourself, how to do it properly, and exactly where the legal limit lies.
Why fouling costs so much
A reversible air conditioner is first and foremost an air heat exchanger. The entire thermodynamics of the system assumes that a nominal airflow passes through the fins of the indoor unit. As soon as that airflow drops — clogged filter, greasy fins, dust-laden fan barrel — three things happen in cascade:
- the temperature difference between supply air and return air increases, so the machine "senses" a demand it cannot satisfy and extends its cycles;
- in heating mode, the high pressure rises, the compressor works in a less favourable range and the real COP falls;
- moisture stagnates in the tray and on the fins, which accelerates microbial colonisation.
The ballpark figures commonly accepted in the trade, notably reflected in ADEME documents on the maintenance of thermodynamic equipment, point to around 5 to 25% excess consumption for an unmaintained unit, the spread depending mainly on the condition of the filters and the heat exchanger. On an air-to-air heat pump providing the main heating for a two-bedroom flat, that easily amounts to €80–200 over a heating season.
There is also a health dimension. ANSES, in its work on indoor air quality, points out that poorly maintained air treatment systems can become sources of bioaerosol emissions — moulds, bacteria — where they are supposed to be neutral. This isn't scaremongering, but it is reason enough not to let a condensate tray fester for ten months.
| Component | Recommended frequency | Who can do the work |
|---|---|---|
| Indoor unit filters | Every 2 to 4 weeks during the season | Occupant |
| Grille and plastic casing | Twice a year | Occupant |
| Indoor heat exchanger (fins) | Once a year | Occupant with care, or a pro |
| Fan barrel and condensate tray | Once a year | Pro recommended |
| Outdoor unit coil | Once a year | Occupant (surface), pro (deep clean) |
| Leak testing of the refrigerant circuit | Depending on refrigerant charge | Certified refrigeration engineer only |
| Topping up or recovering refrigerant | — | Certified refrigeration engineer only |
Step 1: genuinely cut the power
You don't clean a unit that's "on standby". Switch off the dedicated circuit breaker at the consumer unit, not just the remote control: some indoor units keep the motorised louvre and the fan barrel energised, and a fan barrel that starts up while your fingers are inside it hurts a great deal.
Check that there is no voltage before opening the cover. A simple non-contact voltage detector does exactly the job you'd expect of it here, and it costs about the price of a pizza. Also wait five minutes after switching off, to give the capacitors on the board time to discharge.
Step 2: the filters, the thing nobody does often enough
The flat filters in the indoor unit come out by lifting the front panel — almost all wall-mounted Daikin, Mitsubishi, Toshiba, Atlantic or LG models work on the same clip principle.
The correct protocol:
- Vacuum dry first, on the dirty side, with a soft brush. A vacuum with a flat nozzle avoids tearing the mesh.
- Rinse in lukewarm water — never above 40 °C, or the plastic frame will warp.
- If the filters are greasy (open-plan kitchen, smokers), soak them for fifteen minutes with a few drops of washing-up liquid, then rinse thoroughly.
- Dry completely in the shade, laid flat. A filter refitted while still damp means a guaranteed smell within three days.
Never put a filter in direct sunlight or on a radiator: it buckles and lets air bypass the edges, which fouls the heat exchanger directly.
Many units also have secondary filters: activated carbon anti-odour filters, photocatalytic filters, electrostatic cartridges. These generally can't be washed — they're replaced. A set of activated carbon filters for an air conditioner costs a few euros and should be changed once a year; on units where they've been sitting there since installation, the improvement in smell is immediate.
Simple rule: if you can't remember the last time you took the filters out, your unit has been running with excess consumption for months.
Step 3: the indoor heat exchanger, where people get hurt
This is the step where you need to slow down. The aluminium fins of the indoor coil are thin, sharp and fragile. Two classic mistakes:
- Scrubbing: you bend the fins and airflow drops permanently.
- Hosing it down: the water ends up in the electronic board or in an overflowing tray, and finally on the wall.
What does work: a spray-on foaming cleaner made specifically for evaporators, applied from top to bottom, left to act for the stated time, then either rinsed very lightly or not rinsed at all depending on the product — "self-rinsing" foams are designed to drain away through the condensate tray. An evaporator cleaning aerosol for air conditioners remains the safest compromise for a DIYer. Protect the wall and floor with plastic sheeting, and put a bowl under the condensate outlet.
For dry dust before treatment, a soft fin brush or a long-bristled paintbrush is enough, always in the direction of the fins, never across them.
If you see a thick black film, a grey felting over the whole height of the coil, or a visibly loaded fan barrel: stop there. A deep clean of the fan barrel requires partially dismantling the unit, a washing bag and a pressure pump — that's the core of a professional's trade, not a weekend job.
Step 4: the tray and the condensate line
This is the source of 90% of autumn smells, and of water damage too. The indoor unit's tray has been collecting water all summer; by the end of the season it holds a biological deposit which, as it dries out, blocks the inlet of the drain pipe.
What you can do:
- visually check that the accessible part of the tray isn't obstructed;
- gently pour half a litre of lukewarm water into the tray and check that it comes out properly outside, at the bottom of the pipe;
- treat it with a tablet or a bactericidal gel made specifically for condensate trays, which limits biofilm formation during the following season.
What you must not do: push a piece of wire into the condensate line. You'll pierce the flexible pipes, and a leak inside a partition wall only becomes visible once the stain appears on your neighbour's ceiling. If the water won't drain, that's a repair job, using suction from the low point or controlled blowing.
One detail that's often forgotten: if the installation includes a condensate pump, its small reservoir and float foul up in exactly the same way. It's the component that fails silently, turning ordinary condensation into an insurance claim.
Step 5: the outdoor unit before winter
Counter-intuitive but essential: in heating mode, it's the outdoor unit that becomes cold, condenses and frosts up. Its condition therefore has a direct bearing on winter performance.
On the agenda:
- remove leaves, maple seeds, poplar fluff and cobwebs stuck to the coil — a soft brush and the vacuum will do;
- clear at least 30 cm behind and 50 cm in front of the fan; hedges that have grown all summer are the number one cause of lost efficiency;
- check that the drainage under the unit is free and that it doesn't discharge onto a footpath that will turn into an ice rink in January;
- check the condition of the anti-vibration mounts and the tightness of the bracket;
- inspect the insulation on the refrigerant lines: a sleeve cracked by UV means lost performance and condensation on the copper.
If the insulation has deteriorated, a roll of insulating sleeve for refrigeration pipework and suitable tape will sort the problem in twenty minutes. On the other hand, don't wrap the outdoor unit up completely for winter: a reversible heat pump needs to breathe, and a sealed cover fitted over a running machine causes air recirculation and overheating. "Roof"-style covers that only shield from above are acceptable; closed bags are not.
The legal line: where your rights stop
This is the point owners misunderstand most. Cleaning, dusting, rinsing filters, washing a casing: no legislation prohibits any of it — it's routine maintenance.
As soon as you touch the refrigerant circuit, the framework changes radically. The European regulation on fluorinated greenhouse gases — Regulation (EU) 2024/573, which superseded Regulation 517/2014 — and its implementation in French law reserve all handling of refrigerant to operators holding a certificate of competence (attestation de capacité), with staff holding a certificate of aptitude (attestation d'aptitude) in the relevant category. That covers:
- leak testing;
- recovery and transfer of refrigerant;
- any topping up or "recharging" with R-32, R-410A or any other HFC/HFO;
- disconnecting and reconnecting the circuit's fittings.
In practice: the recharge cans sold online for "topping up your air con yourself" are, for a private individual, an illegal operation in France, as well as being technically risky — without gauges or scales, you'll either overcharge or undercharge, and destroy the compressor.
Another obligation worth knowing about: periodic leak testing, the frequency of which depends on the installation's charge expressed in CO₂ equivalent. Small domestic splits, often charged with around 1 kg of R-32, stay below the 5-tonne CO₂ equivalent threshold and are not subject to it. Large multi-split systems and apartment-block installations, however, can cross the threshold and trigger an annual requirement. The equipment log must then be kept up to date and produced in the event of an inspection.
Since 2020 there has also been a requirement for periodic inspection of air conditioning systems and reversible heat pumps rated above 12 kW, every five years, set out in the French energy code (decree no. 2020-912). It applies more to apartment blocks, commercial premises and large single-family-home installations than to standard splits, but many owners are unaware that it applies to them.
What a professional visit really gives you
An annual maintenance contract on a single split unit generally runs between €110 and €180 depending on the region and the number of units. What you're buying isn't the "quick once-over with the vacuum" you could have done yourself, but:
- measurement of high and low pressures, and therefore detection of a drifting charge before a breakdown;
- checks on current draw and on supply/return air temperatures, which reveal a deeply fouled heat exchanger or a tired compressor;
- a full clean of the fan barrel and the tray using a washing bag;
- written traceability, which matters a great deal if you ever need to invoke a manufacturer's warranty or a ten-year structural warranty.
A methodological tip: every autumn, record two simple values yourself, measured at the same spot — the supply air temperature in heating mode at stabilised output, and the unit's power consumption. An indoor thermometer and hygrometer and a plug-in power meter cost around twenty euros each and give you a baseline curve. From one year to the next, a loss of 3 to 4 °C at the supply outlet or a jump in consumption are objective signals, far more telling than a vague impression.
The mini October checklist
- Switch off the circuit breaker, check there is no voltage.
- Remove, wash and dry the filters completely.
- Replace non-washable secondary filters.
- Treat the indoor heat exchanger with foam, protecting the wall and floor.
- Test condensate drainage, treat the tray.
- Clean and clear the outdoor unit, check insulation and mountings.
- Switch the power back on, run it for 20 minutes in heating mode, listen and smell.
- If there's a persistent smell, a new noise, weak airflow or abnormal frosting: call a refrigeration engineer before the first real cold snap.
One last word on timing: demand for callouts explodes in mid-November, when everyone discovers at the same time that the air con no longer heats. In October, you still get to choose your installer and your date. That's probably the strongest argument in this article.
Need an air conditioning solution?
