Split AC not cooling: the checks that come before a gas refill

Updated August 28, 2026 · Claude AC · 2 sources cited

In most Indian households the sequence is the same: the machine stops cooling on the hottest week of May, a technician arrives, and within ten minutes the diagnosis is gas kam hai. Sometimes that is true. Very often it is not, and the reason it gets said so readily is that a refill is the most profitable thing a visiting technician can sell. Running through the checks below first costs nothing, takes about twenty minutes, and puts you in a position to accept or refuse that diagnosis on evidence rather than on trust.

First, decide which problem you have

“Not cooling” covers two very different faults, and confusing them wastes money.

• No cooling at all — the air from the indoor unit is at room temperature. Something has stopped: the compressor is not running, the outdoor fan is not turning, the refrigerant charge is genuinely gone, or the unit is in the wrong mode.
• Weak cooling — cold air comes out, but the room never reaches the setpoint. This is nearly always airflow, heat load or ambient temperature, and almost never a refrigerant problem.

The quick test that separates them: hold a thermometer at the return grille of the indoor unit, then at the outlet, after fifteen minutes of running. A healthy split shows roughly 8 to 12 °C of difference between the two. A gap of only two or three degrees points at capacity or charge; a good gap with a room that stays warm points at heat load, sizing or an escaping-air problem. That single measurement redirects half of all callouts.

The checks, in order

What 45 °C actually does to your AC

An air conditioner does not create cold; it moves heat from inside to outside, and it has to dump that heat into whatever air surrounds the outdoor unit. The hotter that air, the harder the job. Rated capacity is measured at a standard outdoor condition of about 35 °C, while a north Indian afternoon in May sits ten degrees above that — and the air trapped in a shaft or against a west-facing wall can be hotter still. Capacity falls, running time lengthens, and a machine that was comfortably adequate in March feels undersized in May without anything having broken.

Two practical consequences. First, look for a machine specified for tropical conditions — the T3 test point is 46 °C, and units validated there are built to keep working when others cut out. Second, give the outdoor unit air: a shaded position, no enclosure with a single small opening, no stack of two units breathing each other’s exhaust. In dense housing in Delhi or Lucknow, this placement detail decides more summer complaints than any component fault. If the unit is genuinely too small for the room, no service visit will fix it — check the room against our tonnage rules for Indian rooms.

The power supply problem nobody checks

Where the evening voltage sags, a compressor may hum, draw heavy current and cut out on its overload protector, leaving the indoor fan blowing room-temperature air. The symptom reads exactly like a failed compressor. Before condemning anything, watch whether the fault appears only at peak hours, and whether other heavy appliances in the house are also struggling. Most modern inverter machines tolerate a wide input band and no longer need an external device, but older fixed-speed units in weak-supply areas often do — the distinction is set out in our guide to whether a stabiliser is still needed.

Dust and the monsoon

Indian conditions are unusually hard on the heat-exchange surfaces. Pre-monsoon dust storms coat outdoor coils; construction dust does the same year-round; and after the rains, the outdoor coil holds a paste of dust and moisture that insulates precisely the surface that must shed heat. A pre-summer service in March and a rinse of the outdoor coil after the monsoon prevent most mid-season failures — the full seasonal routine is in our guide to AC maintenance in Indian conditions. Coil material matters here too: the corrosion behaviour of coated aluminium versus copper in coastal and industrial air is covered in our comparison of copper and aluminium coils.

When it really is refrigerant

A sealed refrigerant circuit does not consume gas. If the charge is low, there is a leak — at a flare joint, at the service valves, or in the coil itself. The honest indicators are consistent: ice forming on the thinner copper line or on the indoor coil, a hissing or bubbling sound, oily residue at a joint, and a very small temperature split despite clean filters and a clean outdoor coil. What is not an indicator is the calendar. Any technician who proposes an annual top-up as routine maintenance is describing a business model, not a machine. Insist on a leak test before a refill, and on a written note of what was found — the questions to ask, and the pressure readings a serious technician will show you, are in our guide to AC gas refilling in India.

What to say when you call

Describe symptoms, not diagnoses. “The temperature split across the indoor unit is four degrees with clean filters, and the outdoor fan is running” gets you a technician who tests. “It is not cooling, please refill gas” gets you a refill, whether or not you needed one. Ask for the fault to be shown, not narrated: a clogged filter, a dust-caked coil and an oily leak point are all visible. And if the machine is old enough that the repair estimate approaches a meaningful share of a new unit, weigh it against the running cost of a modern variable-speed machine — the arithmetic behind that choice is in our guide to how inverter ACs cut Indian power bills.

Frequently asked questions

My AC is cooling less than last year. Does it need gas every summer?

No. The circuit is sealed, so a genuine loss of charge means a leak that must be found and repaired. A gradual decline over years is far more often clogged filters, a dust-loaded outdoor coil, a fouled indoor coil or a blower that has lost airflow. Clean all of those first and measure the temperature split again before authorising any refill.

How cold should the air from a split AC be?

Judge the difference, not the absolute figure. Roughly 8 to 12 °C between the return grille and the outlet indicates a healthy machine. In a 40 °C room the outlet air will read far warmer than it does in a 28 °C room, which is normal and not a fault.

Why does my AC cool at night but not in the afternoon?

Because capacity falls as the outdoor temperature rises, while the heat entering the room rises at the same time. If the machine holds the setpoint after sunset but loses ground at 3 pm, it is very likely working correctly and simply being asked for more than it can deliver — shading, insulation, sealing gaps, or a larger unit are the answers, not a service visit.

Should I keep the outdoor unit covered or sprinkled with water?

Never cover it while running; it needs free airflow to reject heat. Shading it from direct sun helps. Occasional rinsing of the coil with plain water when the machine is off is genuinely useful, but continuous water sprinkling accelerates scaling and corrosion and is not a substitute for correct placement.

Is a window AC less prone to this problem than a split?

It has fewer joints and a shorter refrigerant path, which slightly reduces leak points, but it is more exposed to dust and the same ambient-temperature physics apply. The broader trade-offs are set out in our comparison of window and split ACs in India.

Read next

• R32, R410A, R22: which gas is in your AC, and why it matters
• The inverter PCB: the other expensive failure in an Indian split AC
• Cassette, ducted or wall split: cooling a shop or a small office
• Error codes and blinking lights: what an Indian split AC is telling you
• Buying a second-hand AC in India: what to check before you pay

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