Air conditioners rarely fail without notice. They get louder, or slower, or start costing more to run, and most people register it as background noise until the day the house won't cool at all.
Calgary makes that worse than it needs to be. Our cooling season runs roughly June to September, so the unit sits idle for the other nine months. Capacitors degrade sitting still, contactor points corrode, and the whole system gets asked to go from nothing to full output on the first genuinely hot day — which is exactly when everyone else's does the same thing and the phones don't stop.
The upside is that almost everything below gives you weeks of warning. Here's what to watch for, what it usually means, and how urgent it really is.
Stop and call — don't keep running it
Three signs mean switch the system off rather than push on.
A burning or electrical smell. Hot plastic, ozone, anything sharp. That points at wiring, the contactor, or a motor overheating. Shut it off at the thermostat and the breaker, and don't run it again until someone has looked.
A breaker that trips more than once. Reset it once. If it goes again, stop. A breaker holding is not the system asking to be reset harder — it's a fault being contained, usually a shorting compressor, a failing capacitor, or a motor drawing more than it should.
Ice on the refrigerant lines or the indoor coil. Ice means the system is running against a blockage or a refrigerant problem, and every hour it runs like that is hard on the compressor. Turn cooling off, set the fan to ON to thaw it, and change the filter while you wait. Don't chip at it — the coil fins bend instantly and the refrigerant tubing sits right behind them. There's more on this in our guide to an AC running with no air at the vents.
Cooling problems
The air isn't cold. The system runs, air moves, but nothing is actually cooling. The usual causes are low refrigerant from a leak, a failed compressor, or an outdoor unit that isn't running at all. Worth checking first: that the thermostat is on Cool and not just Fan, and that the outdoor fan is actually spinning.
It runs constantly and never reaches setpoint. On a 30°C afternoon some continuous running is normal. What isn't normal is never getting there, or taking dramatically longer than it did last summer. That usually points at a system losing capacity — refrigerant, a dirty condenser coil, or an outdoor unit that's been slowly choked by cottonwood fluff and grass clippings.
Some rooms cool and others don't. More often a distribution problem than an AC one — ductwork, dampers, or airflow. Our post on no air coming from the vents covers how to tell which.
The house feels clammy even when it's cool enough. Air conditioning is supposed to remove humidity as a by-product of cooling. When it doesn't, the temperature can read fine while the house feels wrong. That's often an oversized system short-cycling — see why your AC feels humid.
Cycling and running patterns
Short cycling — it starts, runs briefly, shuts off, repeats. One of the more useful early warnings, because it has a wide range of causes from cheap to serious: a dirty filter, a failing capacitor, low refrigerant, or a unit oversized for the house. It also wears the compressor faster than steady running does, so it's worth diagnosing rather than living with. We've covered it in detail in why an AC compressor shuts off after 30 minutes.
The outdoor fan runs but the compressor doesn't, or you hear a hum with nothing turning. Very often a capacitor — a common, inexpensive part that degrades over years of sitting idle through Calgary winters. It's one of the most frequent first-hot-day failures we see.
It won't start at all. Check the obvious first: thermostat set to Cool with the setpoint below room temperature, the breaker, and the outdoor disconnect switch beside the condenser, which sometimes gets switched off during yard work and forgotten.
Noises
A quiet hum and the sound of moving air is normal. These aren't:
- Screeching or squealing — usually a motor bearing, in the outdoor fan or the indoor blower
- Grinding — bearings that have gone past squealing. Running it longer isn't saving you anything
- Banging or clanking — something loose internally, often compressor-related, and usually the expensive kind
- Repeated clicking at startup — a relay or contactor struggling to pull in
- Buzzing at the outdoor unit — commonly a contactor or capacitor on the way out
- Rattling — sometimes just a loose panel or debris in the cabinet, which is the one item on this list you might genuinely fix yourself
Smells
Musty or damp. Moisture sitting somewhere it shouldn't — usually the evaporator coil or a condensate drain that isn't clearing. Left alone it grows into the air you're breathing. Related: why your AC drip pan keeps filling up.
Burning or hot. Covered above. Shut it down.
A faint chemical or sweet smell near the unit can indicate a refrigerant leak. Refrigerant isn't consumed — if it's low, it went somewhere, and topping it up without finding the leak just buys a season.
Water where it shouldn't be
Water pooling around the furnace. Your AC produces condensate, which drains away through a pan and a line. When that blocks, the water finds another route — usually onto the floor, sometimes into the furnace itself. It's rarely dramatic and it's rarely expensive to fix, but it damages things quietly if it's ignored. See AC drip pan problems.
Water stains on a ceiling below an attic unit. Same problem, worse location.
The quiet ones people miss
Power bills climbing with no change in habits. A system losing efficiency runs longer for the same result. Compare this July against last July rather than against June.
It just doesn't feel like it used to. Homeowners are usually right about this and usually dismiss it. Gradual decline is real — a coil fouls slowly, refrigerant leaks slowly, capacity fades slowly.
Hail damage on the outdoor unit. Calgary gets hail, and the aluminium fins on a condenser coil flatten easily. Bent fins choke airflow across the coil and quietly cost efficiency without ever fully stopping the system. Worth a look after any serious storm — it's visible from a few feet away.
Age. Most central AC in Calgary runs 12 to 15 years, sometimes 18 or more with annual maintenance, and our short cooling season means equipment here generally sits at the longer end of the range. Age alone isn't a reason to replace anything. Age plus repairs starting to cluster is.
What's safe to check yourself
- Thermostat set to Cool, setpoint below room temperature, fan on Auto
- The filter — replace it if it's dirty. It's the same filter that served your furnace all winter
- Supply registers open, return grilles clear of furniture
- The outdoor unit clear of grass clippings, cottonwood fluff, leaves and shrubs, with a couple of feet of space around it
- The outdoor disconnect switch beside the condenser
- The breaker — reset once, and only once
That's the list. Past that you're into refrigerant, capacitors and the control board, and none of those are worth improvising with.
What actually prevents most of this
An annual service before the season starts, rather than during it. Cleaning the condenser coil, checking refrigerant pressures, testing the capacitor before it fails on a 32°C afternoon, and clearing the condensate drain are all quick when they're planned and expensive when they're urgent.
The best month to book it is May, for the same reason the worst month to need it is July.
If something on this list sounds like your system, call 587-834-3668 and we'll diagnose it properly rather than guessing. See air conditioning repair for what a visit covers, or AC repair in Airdrie if you're north of the city.
