Air conditioners almost never fail without warning. They fail after weeks of quiet hints that nobody had reason to pay attention to, and then they fail on the first 95-degree Saturday, when every HVAC company in Montgomery County has a three-day backlog.
Here are the five signals that show up first, what each one usually means, and which ones can wait until Monday.
1. The air coming out is not cold enough
Not warm — just not as cold as it was. This is the single most common early sign, and the easiest to talk yourself out of noticing.
You can check it with any kitchen thermometer. Hold it in the airflow at a supply vent for a few minutes, then do the same at the return vent where air is being pulled back in. A healthy system should show roughly a 15 to 20 degree drop between the two. Much less than that and something is wrong.
What it usually means: low refrigerant from a leak, a dirty outdoor coil that cannot shed heat, a failing compressor, or — genuinely, often — a filter so loaded that not enough air is moving across the coil.
Worth knowing: refrigerant is not a consumable. It does not get used up the way gas in a car does. If a system is low, there is a leak somewhere. “Topping it off” every summer is paying annually to refill a bucket with a hole in it. Ask for the leak to be found.
2. It runs and runs and never shuts off
On a brutally hot day a system running nearly continuously is normal — that is what it is sized to do. On an ordinary 85-degree afternoon it is not. A system that never reaches the thermostat setting and never cycles off is working at the edge of its capacity, and the parts wearing out fastest are the expensive ones.
The opposite pattern matters too. Short cycling — kicking on for two or three minutes, shutting off, starting again — is hard on a compressor and points to a control problem, a frozen coil, restricted airflow, or a system oversized for the house.
What it usually means: declining capacity from age, a refrigerant charge problem, a dirty condenser, or duct leakage dumping cold air into an attic or crawlspace instead of a bedroom.
3. Sounds it did not used to make
You know what your AC sounds like, even if you have never consciously thought about it. Trust that. New noises are worth naming, because different noises mean different things and some of them are urgent.
- Hissing or a faint bubbling — often a refrigerant leak. Get it looked at; running low on charge can destroy a compressor.
- Grinding or metal-on-metal screeching — a bearing or a motor. Shut the system off and call. Running it can turn a motor replacement into a compressor replacement.
- Loud click or hum and then nothing — commonly a failed capacitor. Small part, and one of the more satisfying repairs.
- Rattling from the outdoor unit — sometimes debris or a loose panel, sometimes a fan blade out of balance.
- Banging or clanking — something has come loose internally. Turn it off.
If you can safely get a phone near it, record the sound. A ten-second voice memo tells a technician more than a paragraph of description, and it means you are not standing in the basement trying to imitate a noise.
4. The electric bill climbed and nothing else changed
Compare this July to last July rather than July to June — summer bills always rise. If the same month a year later costs noticeably more with the same thermostat setting and roughly the same weather, the system is doing the same work less efficiently.
What it usually means: a dirty coil, low charge, a motor drawing more current than it should, failing capacitors, or simple accumulated age. Efficiency decline is gradual, which is exactly why the bill notices before you do.
5. Water, ice, or a smell
These three get grouped together because all of them mean stop and look rather than wait and see.
Water around the indoor unit
Air conditioning pulls moisture out of the air, and that water is supposed to leave through a condensate drain. A clogged drain line backs the water up into the pan and then onto your floor, your ceiling, or your finished basement. This is the failure most likely to cause damage that costs more than the repair.
If your air handler is in an attic, this is the one to take seriously. A blocked drain there shows up as a stain on a bedroom ceiling.
Ice on the refrigerant line or the coil
Ice looks like the system is working hard. It is the opposite. Ice forms when there is not enough warm air moving across the coil or not enough refrigerant in it, and a frozen coil moves no air at all.
Turn the cooling off and leave the fan running to thaw it. Do not chip at it. Then check your filter, and if the filter was clean, call — because the other causes are a charge problem or a blower issue, and both need gauges.
A smell
Musty means moisture sitting somewhere it should not — usually the drain pan or the coil, occasionally the ducts. Burning or hot-electrical means shut it off at the breaker and call immediately.
Two things to check before you call anyone
Not because we mind coming out, but because you might not need us.
- The filter. Hold it up to a light. If you cannot see light through it, that is very likely your whole problem. Most homes need this changed every one to three months; a house with pets and a forced-air system is at the short end of that.
- The outdoor unit. Clear at least two feet around it. Pull out the grass clippings, leaves and cottonwood fluff matted into the fins. That unit’s whole job is releasing heat into the outside air, and it cannot do it through a blanket of lawn debris.
Also confirm the obvious: thermostat set to Cool and below room temperature, batteries good, breaker not tripped, and the outdoor disconnect switch on. These get missed by everyone, including people who work in the trade.
How much life is left in it?
Residential central air conditioners generally last 12 to 15 years in this climate, sometimes longer with regular service, sometimes less near the coast or in a hard-running installation.
Two age markers matter beyond the number itself. Systems using R-22 refrigerant — the old standard, generally anything installed before about 2010 — can no longer be serviced with newly produced refrigerant, since US production and import ended in 2020. Repairs on those units depend on reclaimed supply and get expensive. And as of 2025, new residential equipment has moved off R-410A to lower-GWP refrigerants under the federal AIM Act phasedown, so if you are replacing this year, ask which refrigerant the new system uses.
If your unit is over 12, uses R-22, and needs a repair in the four figures, that is the conversation where replacement usually wins. Under 10 years with a bad capacitor, fix it and get on with your summer.
Common questions
Should I keep adding refrigerant every year?
No. A system that needs refrigerant annually has a leak, and you are paying repeatedly for the same problem. Have the leak located and priced. Sometimes it is a repairable fitting; sometimes it is the coil, and that changes the decision.
Is one warm room the air conditioner’s fault?
Often not. A single room that will not cool is usually a duct, damper, or insulation issue rather than the equipment. That is good news — it is generally a cheaper fix than anything involving the compressor.
Does a yearly tune-up actually do anything?
It catches three of the five items on this list before they become a no-cooling call: a dirty coil, a weak capacitor, and a condensate drain starting to clog. It will not make an old system new. It does reliably move failures from August to April.
Which of these is an emergency?
Grinding or banging, a burning smell, and water actively running somewhere it can do damage. Shut the system off for those. Everything else on this list can wait for a scheduled visit.
Catch it in the spring, not in August
If your system did any of the five things this summer, that is the useful piece of information. Have it looked at in the off-season, when we can get to you the same week and you are not making a decision in a 90-degree house.
Cozy Home Services is family-owned and based in Lansdale, serving Ambler, North Wales, Harleysville, Hatfield and the rest of Montgomery County. Call (610) 809-6903 or book a visit online.