Air conditioning that has stopped cooling: the European diagnosis order
Contents (7)
The call always comes on the same day: the first genuinely hot afternoon, when the machine that worked perfectly last September is suddenly blowing something that is not cold. In Europe that call has a particular shape, because the equipment is mostly wall-mounted splits and plug-in monoblocs rather than ducted systems, because a large share of those splits are reversible units that spent the winter heating, and because the refrigerant circuit is legally out of bounds to everyone except a certified technician. Working through it in the right order costs nothing and settles most cases before a call-out is even booked.
First, separate two very different faults
Almost every « my air conditioning is not cooling » complaint is one of two problems that share nothing but their symptom, and confusing them wastes the whole diagnosis.
- The air coming out is not cold. Hold your hand under the indoor unit after ten minutes of running. If the stream is room temperature or warmer, the refrigeration cycle is not doing its job: wrong mode, no outdoor unit, a protection trip or a genuine fault.
- The air is cold but the room stays hot. The machine works; it is simply losing to the heat entering the room. That is a capacity, shading or installation question, not a repair.
The second case is far more common than European owners expect, particularly in top-floor flats and rooms with unshaded glazing, and no technician can fix it with a spanner. If your unit produces a clear cold stream but the thermometer refuses to move, the honest answer is in sizing and solar gain — start with our guide to choosing the right cooling capacity in kW rather than booking a repair.
The free checks, in order
1. The mode, which trips more Europeans than any component
A reversible unit that heated the flat in February is often still set to heating, or to fan-only after a cleaning session. Set the remote explicitly to cool (the snowflake, not the sun or the fan), the setpoint several degrees below the room temperature, fan speed to auto, and switch any « eco », « quiet » or « away » preset off for the test. Quiet mode in particular throttles the compressor and outdoor fan and can look exactly like weak cooling.
2. The filters, five minutes and no tools
Lift the front panel of the indoor unit and pull the two mesh screens. If they are grey, the machine has been strangled for airflow and its capacity has been falling all season; a starved coil can also drop below freezing until a sheet of ice blocks it entirely. Wash them in lukewarm water, dry them fully, refit. If you find ice on the indoor coil, switch to fan-only for an hour to thaw it before running the compressor again.
3. The outdoor unit, which is where European installations fail
Go and look at it, and listen. A silent outdoor unit while the indoor one blows means no refrigeration is happening at all. If it runs, check what it is breathing: a condenser boxed into a balcony recess, screened behind a decorative panel, or facing a wall a hand's width away recycles its own exhaust and loses capacity precisely when the outdoor temperature peaks. Clear at least the manufacturer's stated free space in front of the coil, clear leaves and poplar fluff from the fins, and make sure nothing has been stored on top of it over winter.
4. Power and protection
Check the dedicated circuit breaker and, on many European installations, the isolator switch beside the outdoor unit — a residual-current device tripped during a spring storm is a classic cause of « the indoor unit lights up but nothing happens ». Reset once. If it trips again, stop and call someone: a repeated trip is an electrical fault, not an inconvenience.
5. The room itself
Shutters and external blinds closed on the sunlit side, internal doors shut, extractor fans off, and no window left ajar « to let the air circulate ». European homes are frequently cooled with a machine sized for one room while the heat of three rooms flows into it.
Symptom to cause, at a glance
| What you observe | Most likely cause | Who deals with it |
|---|---|---|
| Indoor unit blows, outdoor unit silent | Mode or setpoint, protection trip, capacitor, control board, isolator off | Checks yourself, then a technician |
| Both run, air barely cool, ice on the indoor coil | Blocked filters, fouled coil, fan fault, low charge from a leak | Clean first; if ice returns, a technician |
| Cools in the morning, fails at 3 p.m. | Outdoor unit overheating or recirculating its own exhaust; high-pressure cut-out | Clearance and shading, then a technician |
| Cold air, room temperature unchanged | Undersizing, solar gain, open volume | Shading and sizing, not repair |
| Cooling degraded gradually over two seasons | Slow refrigerant leak, or two seasons of skipped cleaning | Technician with a leak detector |
| Portable monobloc struggles above 30 °C outside | Single-hose design pulling replacement air in through the building | Sealing and venting, covered below |
Heat itself is a diagnosis
A split's rated capacity is measured at 35 °C outdoors. At 40 °C the same machine delivers noticeably less, and its high-pressure switch may cut the compressor out entirely for a few minutes at a time — which owners read as an intermittent fault. During a Mediterranean heat episode a unit that cools well at breakfast and gives up mid-afternoon is usually behaving exactly as designed, at the edge of its envelope, with a condenser that is hotter than the specification ever assumed. Shade the outdoor unit from direct sun without obstructing its airflow, never wrap or spray it, and expect performance to return with the evening.
The plug-in portable deserves its own note, since it is the machine most Europeans own. A single-hose monobloc depressurises the room and drags hot outside air back in through every gap, so its real-world output collapses as the outdoor temperature rises. That is physics rather than failure, and the mitigations — a properly sealed window kit, a shorter hose run, insulating the hose — are set out in our guide to venting a portable air conditioner.
Where your part of the job legally ends
Everything above involves nothing more dangerous than a screwdriver. The refrigerant circuit is different: across the European Union, only personnel holding an F-gas certificate may open, recover, charge or repair a circuit containing fluorinated refrigerant, under Regulation (EU) 2024/573. Venting refrigerant to atmosphere is unlawful. The DIY « top-up » cans sold online for car air conditioning have no place near a domestic split, and using one voids every warranty you hold.
It is worth saying plainly what a technician should and should not propose. A sealed system does not consume refrigerant. If a machine is genuinely low on charge, it has a leak, and the leak is the repair; a recharge without a located leak is a bill for a delay, as our guide to air conditioning maintenance sets out in more detail. Ask for the fault, the part and the leak location in writing before agreeing to anything, and be sceptical of a first visit that diagnoses « needs gas » without a detector ever coming out of the van.
Indicative costs, and your rights before you pay them
European labour rates vary by a factor of two between member states, so treat these as orders of magnitude rather than prices: a diagnostic call-out is typically a modest fixed fee; a capacitor, a cleaning or a drainage clearance sits at the low end; a fan motor or control board is a mid-range job; a coil leak repair with recovery, repair, vacuum and recharge is the expensive one, and on an older machine it is the point at which replacement enters the conversation.
Before paying for a repair, check the calendar. Goods sold to consumers anywhere in the EU carry a legal guarantee against lack of conformity for at least two years from delivery under Directive (EU) 2019/771, and several member states go beyond that floor; this is a statutory right against the seller, entirely separate from any commercial warranty the manufacturer offers. Two practical points follow. Manufacturers' longer commercial warranties on compressors are usually conditional on the installation having been done by a certified professional and on documented servicing — keep the commissioning certificate and the service reports. And where a young machine fails in a way that points to the installation itself, such as a leak at a flare joint made two summers ago, the argument belongs with the installer, not the manufacturer.
Frequently asked questions
Why does my air conditioner blow warm air?
In order of frequency: it is in heating or fan mode after the winter, the outdoor unit is not running because of a protection trip or an electrical fault, the filters are blocked enough to freeze the coil, or the circuit has lost charge through a leak. The first two account for most cases and cost nothing to check.
Does an air conditioner need refrigerant topped up every year?
No. A correctly installed circuit is sealed and keeps its charge for the machine's life. Annual « top-ups » are a symptom of a leak that nobody has looked for, and under EU rules the gas can only be handled by certified personnel in the first place.
How cold should the air from the indoor unit be?
Measure the difference rather than the absolute number: after ten to fifteen minutes of steady running, the air leaving the indoor unit should be roughly 8 to 12 °C below the air entering it. A gap under about 5 °C on a hot day points to airflow or charge; on an inverter unit at low load, however, a small gap can be perfectly normal, so test at full demand.
My unit cools at night but not in the afternoon. Is it broken?
Usually not. Capacity falls as the outdoor temperature climbs, and it falls much faster if the condenser is recirculating its own hot exhaust in a balcony recess. Improve the free space and shade around the outdoor unit before assuming a fault, and check whether the room is simply gaining more heat than the machine was sized for.
Is it worth repairing, or should I replace?
Age and fault together decide it. Small electrical and airflow faults are worth repairing at any age; a sealed-circuit repair on a machine over about twelve years old, especially one running a legacy refrigerant, is usually money spent on a short future — the arithmetic is laid out in our guide to air conditioner lifespan and replacement.
Sources
Read next
- The carbon footprint of cooling a European home
- Cooling a European home without air conditioning: the order that works
- Heat and health in Europe: how cool a home needs to be, and for whom
- Europe’s heatwaves: the record of a continent warming fastest
- Does air conditioning clean the air? Filters, pollen and pollution in Europe