Air Conditioner Running But Not Cooling — What's Wrong?

1. Filter clogged? Slide it out and check — 30% of no-cool calls are just a blocked filter. Wash under running water, dry it, put it back. Five minutes.

2. Outdoor unit fan spinning? If not, the capacitor is likely dead. This is a $150–$250 fix with parts and labour and takes 30 minutes.

3. Ice on the pipework? Turn it off and let it thaw — you've got a refrigerant or airflow issue that needs a technician.

4. Set to cool, not fan or dry? Sounds obvious, but happens. Dry mode in particular is often mistaken for cooling — it dehumidifies without lowering temperature meaningfully.

5. Windows and doors closed? A 5 kW unit can't cool an open house. Also check exhaust fans — a running rangehood or bathroom exhaust will pull conditioned air straight out of the house.

6. Blocked outdoor unit? Grass clippings, leaves, cobwebs and long grass on all sides can starve airflow. Give it 500 mm clearance on every side and a metre out the front.

Setpoint vs reality. Is the room actually warmer than the setpoint? A remote sensor in direct sunlight can read 8°C higher than the room and prevent the system from cooling further.

Age and history. When was the last service? If it's been more than two years, coil fouling alone can cost 20–30% of cooling capacity. A service usually restores most of it.

Modern splits flash a code on the indoor unit LED when something's wrong. Take a photo of the sequence (long flashes vs short) and search your model number plus 'error code'. Most manufacturers publish a lookup table.

Ducted controllers usually show a code on the wall thermostat directly. E1, E5, F3 and P4 are the most common Daikin/Mitsubishi codes we see — they narrow down the fault before we even arrive.

Refrigerant leak at the flare fitting — usually the outdoor unit end. Very common on installs older than 8 years or done cheaply.

Failed capacitor on the outdoor fan — the compressor runs, the fan doesn't, the system ices up.

Dirty condenser coil — outdoor unit can't reject heat, so the indoor coil doesn't cool. Very common in Canberra where pollen and eucalyptus debris coat outdoor units badly in spring.

Stuck reversing valve — the unit is stuck in heat mode even with the remote on cool.

Failed thermistor — the sensor thinks the room is already cold, so the compressor won't run.

If it's still not cooling after those checks, or if you see ice, hear unusual noises, or smell burning — turn it off and book a diagnostic.

The diagnostic fee is typically $180–$220 in Canberra and includes a written fault report. If you go ahead with the repair, most reputable installers roll the diagnostic into the repair invoice.

Capacitor replacement: $150–$280.

Refrigerant recharge + leak repair: $400–$900 depending on where the leak is.

Fan motor replacement: $450–$800.

Compressor replacement: $1,800–$3,200 — at that price, replacement is usually more sensible if the unit is over 8 years old.

Full deep clean and service that restores lost capacity: $280–$420.

On a split: 90% of no-cool complaints trace to filter, outdoor fan, or refrigerant. Three quick checks and you're done.

On a ducted system: add zone dampers stuck closed, blocked return air, kinked flex duct, and thermostat calibration to the list. Ducted diagnosis takes longer because there are more moving parts.

Ducted systems also fail in subtler ways — one room cool, another warm — that a homeowner attributes to the system 'not cooling' when it's actually a duct or zoning problem.

First 2 years: almost always installation defect (flare leak, control error, sensor position).

Years 3–7: filters, capacitor, minor refrigerant top-up territory.

Years 8–12: coil fouling, drain pan corrosion, compressor efficiency loss.

Years 12+: think replacement, not repair, unless the fault is trivial.

Feel the small (liquid) line and the fatter (suction) line during cool mode. Suction should be cold to slightly frosty; liquid should be warm. Both warm = low refrigerant. Both cold = airflow starvation.

Fan not turning: capacitor. Fan slow: motor bearings. Fan noisy: bent blade or debris.

Compressor buzzing without starting: start capacitor failure or seized compressor. Turn it off — repeated starts damage the motor windings.

Filter every 6–8 weeks. Outdoor unit clear on all four sides. Annual service. Fan-only for 10 minutes after heavy cooling. Photograph the outdoor unit yearly for reference.

Homes that do this see roughly 40% fewer no-cool calls, and the ones they do have are usually caught during the annual service before they become emergencies.

Return air grille clean? A blocked return starves the whole system.

Zone dampers responding? Listen for the click of servo motors when zones open and close.

Any zone reaching setpoint faster than others? Points to duct sizing or damper imbalance.

Filter behind the return grille — often forgotten by homeowners because it's not in the ceiling registers.

Model number of the indoor and outdoor units (photo of the label helps).

Age of the system.

What the fault is, when it started, and whether it's intermittent or constant.

Any error codes flashing.

Whether you've had any recent service or electrical work.

The more specific your call, the faster the diagnosis — and the more likely we bring the right part on the first visit.

Same-day diagnostic in Canberra during shoulder season.

Common parts (capacitor, contactor, filter) fitted same day.

Board or sensor: 1–3 working days for parts.

Compressor or coil: 5–15 working days for parts on major brands, longer for older or budget-brand units.

One room warmer than the rest: check the zone damper (open? stuck?), the register (fully open?), and the flex duct (kinked in the roof?). A camera on a rod through the register reveals kinks quickly.

All rooms warm: check the return grille filter, the outdoor unit, and the setpoint on the thermostat. Nine times out of ten it's a filter.

One end of the house always warmer than the other: duct sizing issue. Not usually a repair — it's a design flaw that shows up years later as insulation degrades.

Master bedroom warm at night, cool during the day: solar gain through west windows. The system is fine; you need blinds or external shading.

Fan motor: spins freely by hand when powered off? If not, bearings are shot — replace the motor.

Fan blade: any wobble or damage? A damaged blade destroys the motor within weeks.

Contactor: pull the cover, look for pitting on the contacts. Pitted contactors cause intermittent startup issues.

Capacitor: bulging top? Leaking? Even without visible damage, capacitors weaken with age and are cheap to replace prophylactically at 8+ years.

Refrigerant lines: any oily residue? Oil at joints indicates a slow refrigerant leak.

Base pan: rust holes? Drainage blocked? Standing water rots the compressor mounts.

DIY is worth it for filter, outdoor debris, drainage flushing, and battery replacement — five minutes, zero cost, resolves 30–40% of no-cool complaints.

Anything past that, professional diagnosis is cheaper than trial-and-error parts. A $200 diagnostic saves $500 in mistakenly-ordered parts on average.

If you're mechanically inclined and the unit is out of warranty, capacitor replacement and drain-pan cleaning are within DIY territory. Anything involving refrigerant is not — it's ARCtick-licensed work by law and the fines are substantial.

Unit under 5 years old: repair, warranty likely covers most of it.

5–8 years old, moderate repair (<$800): repair.

5–8 years old, major repair (>$1,500): quote replacement too — sometimes worth it if efficiency has degraded materially.

8–12 years old, moderate repair: repair if it's not a compressor.

8–12 years old, compressor or coil: replace.

12+ years old: replace unless the fault is trivial (capacitor, sensor).

First 60 seconds: read any error codes, check breaker, confirm mode and setpoint.

Next 5 minutes: current draw at the outdoor unit, temperatures at indoor supply and return, refrigerant line temperatures.

Next 10 minutes: check filter, coils, drain, and fan blade. Photograph before/after for the report.

Diagnosis usually complete in 20–30 minutes on a typical no-cool call. Complex or intermittent faults take longer and sometimes require follow-up with a data logger.

COP — coefficient of performance, the ratio of heat delivered to electricity used.

Superheat — how much hotter the refrigerant gas is above its boiling point. Wrong superheat means charge or metering issues.

Subcooling — how much cooler the liquid refrigerant is below its condensing temperature. Another charge indicator.

TXV — thermostatic expansion valve. Meters refrigerant into the evaporator.

EEV — electronic expansion valve. Same idea, controlled electronically. Common on inverter systems.

Reversing valve — the four-way valve that switches between heat and cool modes.

Static pressure — pressure drop across a ducted system's fan. High static pressure means restricted airflow.

Waiting too long — a small refrigerant leak in April becomes a dead compressor in July.

Trying to save money by asking for 'just a regas' — regassing without leak repair means the refrigerant is gone again in weeks.

Accepting a verbal quote for a major repair — always insist on written costings.

Choosing the cheapest quote for a complex fault — the cheapest technician is often cheapest because they skip diagnostic steps.