Why Is My Air Cooler Not Cooling? Desert Cooler Problems in Delhi

First: the free checks, in order

Run these before you call anyone. Between them they explain the large majority of coolers that have stopped cooling, and none of them costs anything.

• 1. Is there water in the tank? Obvious, and still the most common answer. A cooler on a hot Delhi afternoon empties its tank far quicker than people expect, and once the level drops below the pump inlet the pads start drying within minutes. Check the level, not the float indicator, which sticks.
• 2. Put your hand on the pads. Open the side panel or feel through the grille. The honeycomb should be visibly wet, and wet all the way to the top, not just at the bottom. Dry pads mean a cooler that is only a fan.
• 3. Is the pump switch actually on? Almost every cooler has a separate pump switch or knob, marked pump, water or a droplet symbol. Run the fan alone and it blows warm air, exactly as described. This catches more cases than anything else on this list.
• 4. Is a window open? A cooler needs air to leave the room. If every window and door is shut, the room fills with the moisture the cooler is adding and cooling stops almost completely. Open a window on the far side of the room from the cooler.
• 5. Listen for the pump. Switch the fan off and the pump on and stand close. You should hear a low hum and, after a few seconds, water trickling over the pads. Silence means a pump that is not running.
• 6. Try the fan on a lower speed. Counter-intuitive, but true. On the highest speed the air can rush through the pads too fast to pick up much moisture. A medium speed often gives noticeably cooler air.

Why my cooler worked in May but does nothing in August

Because the air outside changed, not the cooler. This is the single most useful thing to understand about the machine, and it is the reason for most of the frustration.

Evaporation only happens if the air has room to take more water vapour. In Delhi’s pre-monsoon weeks the air is fiercely hot and very dry, so a cooler can evaporate a great deal of water and drop the air temperature substantially. Once the monsoon arrives, the air is already close to holding as much moisture as it can, evaporation slows to almost nothing, and the same cooler on the same setting delivers air that is barely cooler than the room — just wetter.

• This is not a fault and no repair fixes it. A new cooler, new pads and a new pump will behave exactly the same way on a humid August evening. Anyone who tells you otherwise is selling something.
• The give-away is the pattern, not the machine. If cooling was strong through May and June and faded as the rains started, that is the season. If it faded over a week, or came and went within a single evening, look for a fault instead.
• A closed room is the same problem, self-inflicted. Sealing the room raises the humidity indoors until the cooler hits its own ceiling in a room that was fine an hour earlier. This is the commonest user error by a distance, and it is free to fix: open a window.
• Cross-ventilation is the design, not a compromise. A cooler wants a path — air in through the cooler, air out through a window or door on the opposite side. Without a way out, the moist air simply recirculates.
• Humid nights are the worst case. Warm, still, humid Delhi nights after rain are when a cooler feels stickiest. On those nights many people run the cooler in fan-only mode with the pump off, which at least moves air without adding moisture.

If your home has an AC as well, this is the honest split: the cooler is the cheap, effective machine for dry heat, and the AC earns its running cost in the humid weeks because it removes moisture rather than adding it. Our guide on AC electricity use covers the other side of that trade-off.

Dry pads: the tank, the pump and the water lines

If the pads are dry while the pump is switched on, water is not reaching them, and that is a real fault with a small number of causes. Switch the cooler off at the socket first.

• The tank is low, or lower than it looks. The pump has to sit submerged. Many coolers stop lifting water well before the tank looks empty, because the pump inlet sits an inch or two off the floor of the tank. Top it up and see if the pads wet through within a minute.
• The pump strainer is choked. The pump has a small mesh cage or filter around its inlet, and in Delhi it clogs with dust, grit and the sediment that settles out of hard water. A choked strainer makes a pump that hums normally but lifts almost nothing. Lift the pump out, pull the cage off, rinse it under a tap and refit.
• The distribution hose has come off or is blocked. Thin flexible pipes run from the pump up to a header at the top of each pad. They slip off their spigots, they kink where they turn a corner, and the small holes along the header block with scale. Look for one pad that is soaked and another that is bone dry — that is a hose or header problem, not a pump problem.
• The pump itself has failed. No hum at all with power on, or a hum with no water anywhere, after the strainer and hoses are ruled out. Cooler pumps are small submersible units and they are a replaceable part rather than a repairable one. This is inexpensive work but it is mains equipment in water, so it is a job to hand over unless you are genuinely comfortable with it.
• The tank is leaking. A tank that needs refilling far more often than it used to, plus a damp patch under the cooler, points at a cracked tank or a perished drain plug rather than an evaporation rate that suddenly changed.

Wet pads but still no cooling: scale, dust and airflow

Here the water is arriving but the machine is still not cooling much. Now the problem is either the pads themselves or the air moving through them.

• Hard water has turned the honeycomb to stone. This is the Delhi failure. Borewell and mixed supply here carries a heavy mineral load, and every litre that evaporates leaves its minerals behind in the pad. Over a season or two the honeycomb goes from soft and springy to hard, pale and crusty. A scaled pad soaks up far less water and blocks air at the same time, so it fails twice over. Press a corner: if it crunches rather than gives, it is finished. Our hard water tips explain why this happens across the whole house.
• Pads are consumable. This is worth stating plainly, because many people try to clean their way out of it. Honeycomb pads are replaced, not cleaned forever, and a set that has done two or three Delhi summers is usually past rinsing. Replacing them is the cheapest big improvement most coolers can get.
• The pads are clogged with dust. Even before scale sets in, Delhi’s dust cakes the inlet face of the pad into a felt. Air cannot get through, so volume drops and the room stops turning over. Gentle rinsing from the clean side outward helps; see our guide on cleaning an air cooler.
• Only part of each pad is wet. A pad wet at the bottom and dry in the top third means water is not being distributed across the top of it — blocked header holes, usually from scale. The dry part passes air without cooling it, which dilutes everything the wet part achieves.
• The fan is moving less air than it used to. Dust builds on the blades and inside the housing, and an old cooler quietly loses air output year on year. Less air means less evaporation and much less cooling reach into the room.
• The cooler is in the wrong place. A cooler works best drawing fresh, drier air — ideally sited at a window or door so it pulls outdoor air in, rather than recycling the room’s own damp air. A cooler in the middle of a sealed room is working against itself.

One more that surprises people: never run a cooler on water that has been standing in the tank for days. Stale water goes slimy, the smell comes straight into the room, and a standing tank is a mosquito breeding site. Drain and refill it.

When to call someone, and what to tell them

Call when the pads stay dry after you have checked the tank, the pump switch, the strainer and the hoses; when the pump makes no sound at all; when the fan runs slowly, noisily or not at all; or when anything about the cooler smells hot, sparks or trips your MCB.

• Say what you already checked. “Tank full, pump switch on, pads dry, no hum from the pump” tells a technician far more than “cooler not cooling” and usually means they arrive carrying a pump.
• Say how old the pads are. If you cannot remember replacing them, say so. Pads and a pump together are the standard revival for a cooler that has done a few Delhi summers, and it is worth asking for both to be quoted so you can decide.
• Anything electrical stays with a professional. Fan motor, capacitor, speed switch, the mains lead, or a cooler that trips the MCB — that is not a home job. It is a mains appliance that sits in water, which is precisely the combination not to experiment with.
• Ask for the tank to be checked for leaks while it is open. It costs nothing extra during a pump job and it saves a second visit.
• Do not accept “the cooler is weak, buy a new one” in humid weather. Ask them to judge it on a dry day, or at least to confirm the pads are wet through and the airflow is strong. A cooler performing normally in August humidity is not a broken cooler.
• Get more than one quote if a whole new unit is suggested. Professionals on this marketplace are independent, they quote you free before starting, and you pay them directly — so there is no cost to hearing a second opinion.

If you are weighing a cooler against an AC for the humid months, our guides on choosing AC tonnage for your room and reducing your electricity bill are the useful next reads. For keeping the cooler itself healthy, see how to clean an air cooler and our summer heat and cooling tips.