AC Not Cooling: 10 Causes and the Ones You Can Fix

The Honest Answer Up Front

An air conditioner that runs but does not cool has one of two kinds of problems: it cannot move enough air, or it cannot move enough heat. That sounds simplistic, but it is the divide every diagnosis starts from, and it is why the first things worth checking are the ones you can check. A clogged filter, a tripped breaker, a thermostat set to fan-only, a condenser buried in hedge trimmings and a slab of ice on the indoor coil are behind a remarkable share of the "AC not cooling" calls we run in a Metro Vancouver July, and every one of them is findable in fifteen minutes with a flashlight and your hand.

When it is not those, it is usually one part: the capacitor, the small silver cylinder that starts the outdoor fan and compressor, is the single most common genuine component failure in residential cooling, followed by contactors and fan motors. Genuine refrigerant problems do happen, but a system does not consume refrigerant, so a low charge always means a leak, and anyone who tops it off year after year without hunting the leak is selling you a subscription, not a repair. For the numbers people actually want up front: the common AC repairs in our flat-rate book run $180 to $450, the $89 diagnostic is credited toward any repair you approve, and a replacement, when the math finally says so, installs at $3,800 to $6,500 for central or $3,800 to $5,500 for ductless.

Do the fifteen-minute checks before you book, because we would rather tell you it was the filter for free over the phone than invoice you eighty-nine dollars to discover it with a flashlight. And when the checks come up clean, stop: capacitors hold lethal charge, refrigerant is regulated, and the diagnostic exists precisely so you do not have to guess deeper.

How an Air Conditioner Cools, in Plain Language

You do not need thermodynamics to diagnose your AC, just the loop. Indoors, a fan blows house air across the evaporator coil, a cold radiator the refrigerant flows through; heat leaves your air, enters the refrigerant, and the now-chilled air rides the ducts back to your rooms. The warmed refrigerant travels outside to the condenser, where the compressor squeezes it hot, the outdoor fan blows air across the condenser coil to dump that heat into the street, and the refrigerant comes back inside cold to repeat the cycle. Cooling is heat moving, on a conveyor belt of refrigerant, from your living room to your patio.

Every failure in Chapter 3 is one link in that chain going weak. If the indoor fan cannot push air across the coil, you get weak airflow, a frozen coil, or both. If the outdoor fan or compressor will not run, the loop stalls and the indoor coil stops getting cold refrigerant, so air blows room-temperature. If the refrigerant has leaked out, there is not enough conveyor belt to carry the heat, and the coil runs too cold, freezes, and cools nothing. If the filter is clogged, the coil starves for air and ices over even with a full refrigerant charge. Once you can name the links, the ten causes stop being mysterious.

One term worth knowing because it appears on quotes: the two copper pipes at the outdoor unit. The fat one, the suction line, should be cold and sweating on a healthy system. The thin one, the liquid line, should be warm-to-hot. A warm fat pipe means the loop is not carrying heat; a frozen fat pipe means the charge or the airflow is off. Both readings are on the honest diagnostic checklist.

The Ten Causes, Ranked by Likelihood

Ranked by how often we actually see them in Metro Vancouver, from the ones that cost you a flashlight battery to the ones that cost you a decision. The Fix It Yourself column is honest: four of the ten are yours, six belong to a licensed tech, and the boundary between them is safety, not skill.

The Frozen Coil: the Symptom That Hides Its Cause

A block of ice on the indoor coil looks catastrophic and is usually a two-cause problem: either too little air crossed the coil, or too little refrigerant circulated through it. Both make the coil temperature drop below freezing, and the condensation on the fins freezes instead of draining, until the ice bridges the coil, blocks airflow entirely, and the AC blows room-temperature air while working harder than ever. Running a frozen system does real damage, because liquid refrigerant can slug back to the compressor, and the compressor is the part worth protecting.

The homeowner move is thaw-and-retest, from Chapter 4: cooling off, fan on, wait, fresh filter, one honest retest. If the freeze comes back, the cause is under the charge or inside the blower, and the $89 diagnostic earns its fee, credited to the repair. The technician will read the pressures, check the charge against the nameplate, measure airflow, and tell you which side of the divide you are on. What the tech will not do, on our crews, is simply melt the ice and leave: a freeze-up without an explanation is a symptom, and we write down which cause we found.

The Capacitor: the Part That Fails Most

The capacitor is the small oval or round cylinder in the outdoor unit's electrical panel, and its job is brutal: it stores and dumps a heavy jolt of current to start the compressor and fan motors, thousands of times a season, in a metal box that sits in the sun all July. Capacitors weaken with heat and age, and a weakened capacitor produces the single most recognizable not-cooling signature in residential cooling: the outdoor unit hums, because power is arriving, but the fan will not start, because the start torque is gone.

The visible signs are a fan that starts when you nudge it with a stick, a unit that starts and runs for minutes then dies, or a bulged or domed capacitor top, visible through the panel grille on some units. Here is the boundary that matters, plainly: this is not a DIY part, ever. A capacitor holds a serious stored charge with the breaker off, and it can put an untrained hand in the hospital on a system that is completely unplugged. The part itself is modest; the skill is discharging it safely, matching its rating exactly, and confirming the motor and contactor were not collateral damage. In our flat-rate book, capacitor work lands with the common AC repairs, $180 to $450, and the $89 diagnostic that identified it is credited to that invoice.

One more honesty note on capacitors: they are also the industry's favourite upsell. A tech who condemns a capacitor without testing it with a meter, or who replaces one on every visit, is guessing. Ask for the microfarad reading, written on the invoice, and compare it to the rating printed on the part. Ours always appear, because that is how you keep a 4.9-star rating over 39 reviews.

Refrigerant: the Honesty Test for Any AC Company

Refrigerant is the conveyor belt, and an air conditioner does not burn it, consume it or use it up. A sealed system holds the same charge for decades. So the sentence "your AC is low on refrigerant" only ever means one thing: it leaked, and it leaks somewhere specific, at a fitting, a coil, or a corrosion pinhole in a line. The honest response to a low charge is a leak search, electronic detection, UV dye or pressure isolation, then a quoted repair, then a weighed-in recharge to the nameplate charge.

The dishonest response is the annual top-up: add some refrigerant, cool the house for a season, repeat next July. It costs you a subscription, vents regulated refrigerant to the atmosphere year after year, and postpones the small repair until it becomes a compressor. If a company proposes ongoing top-ups without a leak search, or quotes a recharge with no pressure readings and no hunt for the source, that is the honesty test failing in real time, and the second opinion is cheaper than the third season of top-ups. Our AC repair crews in Vancouver and the teams covering Surrey and the Fraser Valley run leak searches as standard practice on every low-charge diagnosis, and the findings go on the invoice.

One forward-looking note for owners of older systems: the industry is mid-transition away from R-410A toward lower-GWP refrigerants, which matters at replacement time and barely matters mid-life. A leak on an older system is usually repairable; it is simply worth knowing, before you spend on a large refrigerant repair, that the replacement path, $3,800 to $6,500 for central or $3,800 to $5,500 for ductless, is the moment the new refrigerants and the rebate-eligible heat pump equipment enter the math.

When the Answer Is Replacement, Honestly

Three facts retire an air conditioner. Age, first: in Metro Vancouver's short but intense cooling season, 12 to 15 years is the honest horizon, and units that limped through the heat-dome years are aging faster than their birth certificates say. The compressor, second: a failed compressor on an out-of-warranty unit is a replacement conversation, because putting the most expensive part in a decade-old system is financing a decline. The refrigerant economics, third: a major leak repair on legacy equipment, weighed against equipment whose efficiency has moved on, tips the same way.

The replacement math, from the same flat-rate book as the repairs: a new central air conditioner installs at $3,800 to $6,500, sized to the house with a load calculation, not to the old unit's nameplate; a ductless system, one outdoor unit and one wall head, installs at $3,800 to $5,500 and solves the one-room problem with cold airflow; and multi-zone ductless covers a whole floor plan. And because every ductless head is also a heat pump, the heat pump question belongs in the same conversation: combined CleanBC Better Homes, BC Hydro, FortisBC and municipal top-ups can reach $16,000 for cold-climate heat pumps in 2026, we complete the paperwork, and the heat pump pages lay out the equipment and eligibility side of that decision.

The decision rules, compressed: under 10 years old, repair almost anything in the $180 to $450 band; 10 to 12, repair the cheap faults and start planning; past 12 to 15, or a compressor, or a major leak, replacement wins on total cost of ownership. Financing runs from 7.99 percent with approved credit for the day the answer is replacement, and the same cooling service teams across Metro Vancouver quote repairs and replacements from one book, so the numbers land side by side instead of in competing pitches. If the diagnostic discipline in this guide sounds familiar, it is the same framework we published for heating season in the furnace not working guide, and for the weeks when the whole region is testing its cooling, the heat dome preparedness guide covers the house-side playbook.

Prevention: the May Visit That Skips the July Queue

Metro Vancouver's cooling season is short, which makes its failure calendar brutally concentrated: the first sustained 28-degree week, when every AC in the region starts at once after ten idle months, is when capacitors fail, filters reveal themselves and condensers meet the hedge trimmer. A May maintenance visit before that week is the air-conditioning version of the October furnace tune-up, and it covers the same ground a diagnostic covers: coil condition, capacitor microfarads, contactor contacts, refrigerant pressures against the nameplate, condensate drain flow and temperature split across the coil.

Between visits, the homeowner list is short and free: fresh filters on a wildfire-smoke-aware schedule, thirty centimetres of condenser breathing room with the hedge cut back, nothing stored or dumped on or beside the outdoor unit, the two-pipe hand test once or twice a season, and a note of anything odd, humming, slow starts, weak airflow, because the note is what turns a July emergency into a May line item. If the system is already acting up, do not wait for the calendar: the $89 diagnostic is available year-round and is credited toward any repair, and the 24/7 line, 604-615-2212, answers heat-wave nights with a flat $150 after-hours premium posted in advance.