It's the most common call we take every summer across Stoke-on-Trent and the wider Midlands: the air conditioning is switched on, the fan is running, but the room just isn't getting cold. Sometimes the fix takes five minutes and costs nothing. Sometimes it's a fault that legally has to be handled by an F-Gas certified engineer.
Here are the seven causes we diagnose most often, roughly in the order we check them — including which ones are safe to look at yourself before you pick up the phone.
1. Dirty or blocked filters
The simplest and most common culprit. The filters inside your indoor unit catch dust continuously, and once they clog, airflow across the cooling coil collapses — the unit runs flat out while barely moving any air. If you can't remember the last time the filters were cleaned, start here: most wall-mounted units let you lift the front cover and slide the filters out for a rinse. If cooling improves immediately, book a proper service and deep clean to deal with the dust that's already reached the coil.
2. Low refrigerant from a slow leak
If the system blows air that's only slightly cool, or you can see ice forming on the pipework, low refrigerant is the likely cause — and refrigerant only gets low because it's leaking. This is the one fault where UK law is very specific: under the F-Gas Regulations, an engineer must find and repair the leak and confirm the system holds pressure before recharging it. Anyone offering to simply "top up the gas" over the phone is proposing something illegal as well as pointless, because the new refrigerant will leak out the same way.
We carry out the leak test, repair and regas as a single visit wherever possible — see our air conditioning repair service in Stoke-on-Trent for how the process works.
3. A failed capacitor
The capacitor gives the compressor and fan motors the jolt they need to start. When it fails — and heatwaves are exactly when they fail, because heat is what kills them — the outdoor unit may hum without starting, click repeatedly, or the indoor fan will run while the outdoor unit does nothing. The part itself is inexpensive and a certified engineer can usually replace it on the first visit; our vans carry common capacitor sizes for exactly this reason.
4. A frozen evaporator coil
Counter-intuitively, a unit that's iced up inside can't cool your room. Freezing is a symptom rather than a fault in itself — it usually points back to restricted airflow (those filters again) or low refrigerant. If you spot ice on the indoor unit or pipework, switch the system off and let it thaw fully before doing anything else, and don't chip the ice off. If it refreezes after a thaw and a filter clean, the underlying cause needs diagnosing professionally.
5. A blocked condensate drain or failed pump
Cooling air produces condensation, which drains away through a small pipe — often helped by a little pump. When the drain blocks or the pump fails, many units shut the cooling down deliberately to stop water pouring down your wall (and some do it anyway). Water dripping from the indoor unit, a gurgling noise, or cooling that cuts out after a few minutes all point this way. It's one of the quickest professional fixes on our list.
6. Controller settings and sensor faults
It sounds obvious, but we resolve a surprising number of call-outs by finding the system in "fan" or "dry" mode rather than "cool", or with a schedule that's overriding the remote. Check the mode icon (usually a snowflake for cooling) and the setpoint temperature first. If the settings are right but the unit behaves erratically — short bursts of cooling, wildly wrong room temperature readings — a faulty temperature sensor is a candidate, which is a diagnostic job.
7. A struggling outdoor condenser
The outdoor unit needs to dump the heat it removes from your room. If it's wrapped in garden debris, hemmed in by storage, coated in poplar fluff, or baking in direct sun against a wall with no airflow, its capacity drops sharply on the hottest days — precisely when you need it most. Keep a clear space around the unit and gently clear any visible debris from the coil fins. Persistent poor performance after that deserves a professional clean and inspection.
When to call an engineer
Filters, settings and clearing the outdoor unit are safe DIY checks. Anything involving refrigerant, electrical components or repeated freezing is engineer territory — both for safety and because refrigerant work without F-Gas certification is illegal in the UK.
Airtastic's F-Gas certified engineers diagnose and repair all major brands — Daikin, Mitsubishi Electric, Samsung, LG, Fujitsu, Toshiba, Panasonic and Haier — across a 50-mile radius of Stoke-on-Trent, including Newcastle-under-Lyme, Stafford and Crewe. Most faults are identified and quoted on the first visit, and no chargeable work goes ahead without your say-so.
Call 0330 043 9244 or book a diagnostic visit — in summer we prioritise commercial breakdowns and vulnerable residential customers.