AC Not Cooling? 10 Reasons and How to Fix It

This is the single most common AC not cooling reason across every brand we service — and the most avoidable. The filter is just a mesh panel sitting inside the indoor unit — its job is to catch whatever is floating in your room air before it reaches the coil inside. In India, particularly in dusty environments, filters choke up in 2 to 3 weeks during heavy summer use.

When a filter is blocked, airflow across the evaporator coil drops sharply. The coil cannot absorb heat from the room. The AC runs at full power but the room temperature barely moves. Electricity consumption goes up while cooling goes down — the worst possible combination.

There is another consequence that most people do not know: a severely blocked filter causes the evaporator coil to freeze (see Reason 6). What started as a simple filter issue becomes a frozen coil that needs a technician visit. All of this is preventable.

Fix it yourself: Open the front panel of your indoor unit — it usually swings up or unclips without tools. Slide out the filter. It is that mesh panel, usually grey or white. If it is dark grey, brown, or matted with dust — rinse it under a tap. Let it dry completely in shade for at least 30 minutes. Never put a wet filter back in. Slide it in, close the panel, and restart the AC. This single step restores 15 to 25% cooling efficiency in most cases.

How often: Every 2 to 3 weeks during summer. Once a month during cooler months. In particularly dusty locations, once a week is not excessive.

This gets more calls than people expect. The AC remote has multiple modes — Cool, Fan Only, Dry, Auto, and sometimes Heat on newer inverter models. If someone pressed the wrong button, the unit will run — the fan will blow — but no cooling happens because the compressor is not engaged.

Fan Only mode catches more people than you would think. The indoor unit blows hard, the vents are pushing air, everything looks like it is working — but the outdoor unit is dead silent. No compressor running, no cooling happening. The room stays exactly as hot as it was. We have had customers call us convinced their compressor had failed, and the fix was pressing the Mode button once — the simplest AC not cooling reasons there are.

Fix it yourself: Hit Mode on the remote till you see the snowflake. Then look at the temperature — if the room is 30°C and you’ve set 28°C, the compressor has almost nothing to work with. Push it down to 20°C or 22°C. Give it 15 minutes. Nine times out of ten, that’s the whole problem.

Also check the remote batteries. A weak battery can send partial signals, causing the AC to enter the wrong mode without you realising it.

The outdoor unit is where your AC throws the heat it pulls from your room. If that heat has nowhere to go — walls too close, stuff stacked around it, fins choked with dust — the whole system just stops cooling properly. A blocked outdoor unit is one of the most overlooked AC not cooling reasons we come across.

In ground-floor homes we regularly find the outdoor unit buried behind gas cylinders, old buckets, or whatever else got dumped in that corner over the years. In first-floor installations, dust and cottonwood (poplar seeds in spring) can mat the condenser fins solid. In both cases, the AC compressor works harder, draws more current, and delivers less cooling — exactly the opposite of what you want.

Fix it yourself: Walk outside and look at the unit. There should be at least 30 cm of clear space on all sides, and ideally 1 metre of clearance on the outlet side (where the fan blows). Remove any stored items. Use a dry soft brush to clean the fins from outside. If the fins are caked, a light spray with a garden hose (low pressure, not jet mode) clears them effectively. Do not use a pressure washer — it bends the fins. After clearing, restart the AC and compare the cooling.

This is not a fault — it is a mismatch. A 1-ton AC is designed for a room of roughly 100 to 120 square feet with standard ceilings and reasonable insulation. A 1.5-ton handles 150 to 180 square feet. But these numbers assume average conditions. In India, several things push heat load higher than the rule of thumb accounts for.

South or west-facing rooms with large glass windows absorb significant solar heat in the afternoon. Rooms with RCC rooftops on upper floors get conducted heat from the slab throughout the day. Older homes with lime plaster walls and no roof insulation gain heat faster than modern construction. A 1.5-ton AC in a 160 sq ft room with a west-facing glass wall and an exposed RCC roof may genuinely struggle between 2 pm and 6 pm in May — even if the AC itself is perfectly healthy.

What helps without replacing the AC: Before assuming something is broken, try the cheap fixes first. Heavy curtains on the west or south-facing windows make a real difference — afternoon sun through glass dumps heat directly into the room the AC is trying to cool. Close the gaps under doors so cold air isn’t bleeding out constantly. Switch off the TV, laptop, and anything else generating heat near the unit. Run a ceiling fan alongside the AC — a 25°C room with moving air genuinely feels like 22°C. Do all of this before calling anyone.

Refrigerant gas is what actually moves heat. The compressor pushes refrigerant around a closed loop — it picks up heat from your room at the indoor coil, carries it outside, dumps it there, and comes back for more. When gas leaks anywhere in that loop, the system can’t carry enough heat out. The AC runs fine on paper but the room stays warm. Low refrigerant is among the more serious AC not cooling reasons because it never fixes itself.

Here is something important that technicians often do not explain clearly: refrigerant in a properly working AC never runs low. It is a sealed system. If your AC is low on gas, there is a leak — from a loose flare fitting, a pinhole in the copper pipe, a damaged valve, or a manufacturing defect. Topping up the gas without finding and fixing the leak is like filling a punctured tyre with air. It will be low again in 4 to 8 weeks.

What a proper repair looks like: The technician connects gauges to check the system pressure. If low, they use a leak detector or soap solution to find the exact source. The leak is sealed first — then the system is vacuumed to remove air and moisture, then recharged to the correct pressure for your specific model and refrigerant type (R22, R32, or R410A). Any technician who skips the leak detection step and just adds gas is cutting corners at your expense.

Approximate cost: ₹1,200 to ₹2,800 depending on refrigerant type, quantity needed, and leak repair complexity.

Most people don’t believe this until they see it. In 46°C heat outside, the coil inside your indoor unit can literally freeze solid. It happens when airflow drops too low — the coil surface goes below zero and ice builds up on it. Once that happens, it can’t absorb heat from the room anymore. The AC runs at full power and blows air that feels like nothing.

The irony: the two most common causes of a frozen coil are a clogged filter (Reason 1) and low refrigerant gas (Reason 5). So this is often a downstream consequence of something that started simple and was left unattended.

What to do immediately: Switch the AC off at the remote. Switch it to Fan Only mode and let it run for 20 to 30 minutes — this melts the ice without the compressor running. Do not turn the cooling back on until all ice has melted. Then clean the filter. If the coil freezes again the following day, the root cause has not been fixed and you need a technician to check the refrigerant and do a full coil inspection.

Critical warning: Running an AC with a frozen coil for extended periods forces the compressor to work against abnormal pressure. This converts a ₹500 coil cleaning into a potential ₹15,000 compressor replacement. Switch it off the moment you suspect freezing.

Even when the outdoor unit looks presentable from the outside, the internal condenser coils — the dense metal fins through which the fan pushes air — can be coated with years of compressed dust, oil residue, and grime. When the coils are caked up, the outdoor unit can’t throw the heat out properly. The refrigerant goes back into the compressor still carrying heat it was supposed to dump outside. This AC not cooling reasons makes cooling quietly get worse over months — most people only notice when they think back and realise last summer wasn’t this bad.

This is a gradual problem, which is why people often miss it. They assume the AC is just aging when in reality a proper coil wash restores performance close to new.

A technician uses a chemical coil cleaner or a pressure washer at controlled pressure to wash the condenser fins from inside out. This is one of the core tasks in an annual AC service and the primary reason we recommend getting the full service done in February or March before summer starts — not in June when a waiting list is already forming.

Approximate cost: ₹500 to ₹900 for a condenser wash included in a full service. Standalone condenser wash ₹300 to ₹600.

This is a particularly Indian problem. ACs are designed to operate at 220V to 240V. In many residential areas — especially older colonies, semi-urban localities, and areas with overloaded distribution transformers — voltage can drop to 160V to 180V during peak summer hours when the grid is under maximum load. At these voltages, the compressor struggles to start, runs at reduced capacity, or cuts out entirely through its internal protection relay.

Data from the Central Electricity Authority shows that monsoon months see 2.3 times the voltage anomaly incidence compared to dry months, making electrical issues a bigger factor in July and August than people realise.

Inverter ACs have another problem with bad power — the PCB and the variable-frequency drive inside are sensitive components. One bad surge and the board can get damaged even if the unit seems to survive it. You won’t always know immediately. The fault shows up days later when the AC stops cooling properly for no obvious reason

What helps: A properly rated voltage stabiliser — 5 KVA for 1.5-ton AC, 8 KVA for 2-ton — protects the compressor and PCB from both undervoltage and overvoltage. Most new inverter ACs handle 160V to 264V on their own. Older units and non-inverter models don’t — they need a stabiliser. Also worth getting an electrician to check the dedicated circuit while they’re there — wrong wire gauge or a mismatched MCB rating causes more problems than people realise.

Approximate repair cost: ₹400 to ₹1,500 for electrical connection work. Voltage stabiliser: ₹2,500 to ₹5,000 depending on capacity.

The start and run capacitors are small cylindrical components that give the compressor motor and the outdoor fan motor the initial burst of energy needed to start, and the sustained power to keep running efficiently. When a capacitor weakens or fails — which happens more often after voltage spikes, or simply with age in non-inverter ACs — the motor it serves cannot start properly or runs at reduced efficiency.

A failed capacitor is a common AC not cooling reason — and one of the cheaper ones to fix: the outdoor unit tries to start, makes a clicking or humming sound, and then shuts off without the compressor fully engaging. The indoor unit continues to run normally, blowing air — but without the compressor, there is no refrigerant movement and no cooling. Some ACs will keep trying and keep failing repeatedly. Others lock out and show an error code.

Capacitor replacement is a straightforward job for a trained technician — it typically takes 20 to 30 minutes. The part costs between ₹150 and ₹400 and labour is minimal. Total repair cost is usually ₹500 to ₹1,200. It is one of the cheaper AC not cooling repairs and worth diagnosing early rather than assuming a compressor fault.

Compressor fault is the most serious AC not cooling reason — and the most expensive. It pressurises the refrigerant and drives the entire cooling cycle. When the compressor fails — whether through winding failure, seized bearings, or a mechanical fault — the AC simply cannot cool at all. No amount of filter cleaning or gas refilling will help because without the compressor operating, refrigerant does not circulate.

On inverter ACs, the PCB (Printed Circuit Board) controls the compressor’s variable-speed drive. A PCB failure can either prevent the compressor from starting entirely, or cause it to run erratically — resulting in poor or inconsistent cooling. PCB faults are more common after sustained voltage spikes, monsoon humidity getting into the outdoor unit, or simply age on units over 8 to 10 years old.

Repair vs Replace — the honest calculation: Compressor replacement is expensive: ₹6,000 to ₹20,000 for the part alone, plus labour. PCB replacement: ₹2,500 to ₹8,000 depending on brand and model. Before agreeing to either repair on an older unit, ask your technician for the AC’s age and whether the repair cost exceeds 50% of a new AC’s price. On a unit over 8 years old, with a non-inverter compressor, replacing the entire AC with a 5-star inverter model often makes more financial sense — you recover the cost in electricity savings within 2 to 3 years.

Our technicians always give you this calculation honestly before recommending a repair. We do not have an incentive to oversell expensive repairs on dying units.