Why Is Your AC Not Cooling? 8 Real Causes and What to Check

An air conditioner that powers on, blows air, but does not bring the room down is one of the most common complaints we attend in Haridwar. The good news is that the cause is usually one of a small number of things, and several of them you can check yourself in under ten minutes — without opening the unit.

This guide walks through the eight causes we see most often, in the order we usually diagnose them, and tells you which signs point to which cause. It is written to help you make a smarter call, not to replace a proper diagnosis on site.

First, work out which problem you actually have

These are three different faults that people all describe as "the AC is not cooling". Telling them apart saves time:

• Not cooling at all — the compressor is not running, or the unit cannot make cold air. This is the situation this article covers.
• Cooling, but weakly — air comes out slightly cool instead of genuinely cold. Usually a refrigerant charge problem or a long-neglected filter.
• Cooling then stopping after a while — works for ten minutes, then blows warm air. Often an overheat protection trip or a coil icing up and then thawing.

8 causes of an AC that is running but not cooling

1. Thermostat or mode is set wrong

The cheapest and most common explanation. Check that the unit is in Cool mode (not Fan, Dry or Heat), that the temperature is set well below room temperature — around 24–26°C is a sensible setting — and that the fan speed is not fixed at the lowest setting. On window units a knob can easily be nudged out of position. This costs nothing and fixes a surprising number of calls.

2. Dirty or blocked air filter

A filter choked with dust restricts airflow across the indoor coil. When airflow drops, the coil ices over, and an iced coil cannot transfer heat — so the unit runs, feels like it is working, and delivers warm air. Lift the front panel and slide the filter out; if it is grey, matted or visibly thick, that is your answer. Rinse it with lukewarm water, let it dry fully, and refit it. Never use hot water, which warps the plastic frame.

3. Low refrigerant charge (the classic "gas refill")

Refrigerant is a sealed loop; it does not get "used up" on its own. If pressure is low, it is almost always because of a leak somewhere — a corroded copper line, a worn flare nut, a puncture from a sharp rod in an outdoor unit, or a failing valve.

Signs that point to a leak: cooling that has got steadily weaker over weeks or months; the outdoor unit's copper lines sweating or frosting while the indoor unit blows warm; a hissing or gurgling noise near the outdoor unit; a constantly running compressor with no cooling gain.

This is why "gas filling" alone is a poor fix. Topping up a leaking system means you will be back within months, and each top-up costs more because the refrigerant charge keeps dropping. The correct job is to find the leak, repair it, pressure-test, and only then recharge.

4. Compressor fault

The compressor is the pump that drives the whole cycle. When it fails it typically stops running entirely, and you may hear a hum from the outdoor unit with no fan spin, or nothing at all. Other compressor-related symptoms: the unit trips the breaker, the outdoor fan runs but the compressor does not, or a burnt electrical smell comes from the outdoor unit. A failed compressor is not a consumable — it usually means replacing the compressor or the outdoor unit. A technician can confirm with a clamp meter and pressure readings, and we will tell you honestly if the repair no longer makes financial sense.

5. Capacitor failure (very common, and affordable)

The run capacitor is a small component that gives the compressor its starting push. When it goes bad — often just from age and heat — the compressor tries to start, fails, and the unit may hum, click repeatedly, or trip its safety cutout without ever delivering cold air. This is one of the most frequent causes of "the AC suddenly stopped working" and also one of the more affordable repairs, because the part itself is inexpensive. Replacing it involves working with live mains voltage inside the outdoor unit, which is not a DIY job.

6. PCB / electronics fault

Modern ACs run on a control board. A failed relay, a dry joint, or a failed sensor on that board can stop the unit responding, cause a display error code, or make the compressor never start even though everything mechanical is fine. Symptoms include a blinking error code on the display, the unit ignoring the remote, or a fan that runs erratically. Board-level repair is sometimes possible and sometimes cheaper than a full board replacement — a technician will test and tell you.

7. Outdoor fan motor or indoor blower fault

Both sides need airflow. If the outdoor fan is dead, the condenser cannot reject heat and the compressor will overheat and trip out — often after a while, not immediately. If the indoor blower is dead or seized, you get weak or no air at all. A fan motor that squeaks, rattles or drags usually needs bearings or lubrication, and one that is completely silent has usually failed electrically.

8. Drainage blockage (and what it looks like)

If the indoor coil ices up, the water that forms has to drain away through a small tube. Block it with algae or dirt and the water backs up and overflows — you see dripping water on the floor or wall, sometimes mistaken for a leak. Clogged drains also raise humidity inside the unit, which encourages the icing in the first place. This shows up heavily in humid months and in units that go long between services.

What you can safely check yourself

• The mode, temperature setting and fan speed.
• The filter — clean or replace it.
• Is the outdoor unit running at all (fan noise, any hum)?
• Any error code displayed on the indoor unit?
• Any water dripping near the indoor unit?
• Is the unit tripping your breaker?

Leave everything else to a technician. The outdoor unit contains live mains voltage, the refrigerant circuit is under high pressure, and both are genuinely dangerous to open.

When to book a technician

Book a visit if any of these apply:

• Cleaning the filter did not restore proper cooling.
• The outdoor unit is completely silent, or hums and clicks without the compressor running.
• Cooling has been gradually getting weaker over weeks or months — this points to a leak, not a top-up.
• You see frosting or sweating on the copper lines, or water dripping from the indoor unit.
• The unit trips the breaker, smells burnt, or shows an error code.
• You hear grinding, rattling or a repeated clicking sound.

How to reduce the chance of it happening again

• Clean or change the filter every few weeks in summer, less often otherwise.
• Get the unit serviced before peak summer, not during it.
• Keep the outdoor unit clear of debris and ensure it has shade and airflow around it.
• Run the AC at a sensible temperature — around 25–26°C — instead of 16°C. Very low setpoints run the compressor near-continuously and wear it out faster.
• Use a voltage stabiliser in areas with unstable mains supply; power surges are a common cause of sudden board and compressor failures.

Get it checked in Haridwar

If you are in Haridwar, nearby areas, or anywhere in Uttarakhand, Kraps Care (Kurhi Refrigeration & Power Solutions) can diagnose and repair your AC — split, window, cassette and commercial units. We can also take on an annual maintenance contract so this is planned rather than emergency work.

Kraps Care — AC repair, refrigeration and power equipment service in Haridwar. This article is general guidance written by our technicians; every machine is different and only an on-site check can confirm the actual cause. See also: why your refrigerator is not cooling and how to spot a refrigerant leak.