Why is my AC running constantly but not cooling?

Your AC running constantly without cooling is one of the most common summer complaints we hear in Ottawa — and it almost always points to one of a handful of fixable issues.

Start with the basics before calling for service. Check your air filter first — a clogged filter restricts airflow so severely that the system can't transfer heat properly, causing it to run endlessly without results. If the filter is grey and matted, replace it immediately (1-inch filters should be changed every 1-3 months). Also check that all your supply and return vents are open and unobstructed by furniture.

The most common culprit is low refrigerant. Your AC uses refrigerant to absorb heat from your home's air. If there's a leak, refrigerant levels drop and the system loses its ability to cool effectively — but it keeps trying, running non-stop. You might also notice ice forming on the refrigerant lines or the outdoor unit. This is not a DIY fix; refrigerant handling requires an EPA/TSSA-certified technician, and the leak needs to be found and repaired before recharging.

Other likely causes include a dirty condenser coil (the outdoor unit), a failing compressor, or a system that's simply undersized for your home. Ottawa summers have been getting hotter, and older systems sized for milder conditions can struggle during heat waves above 30°C. A frozen evaporator coil (indoor unit) is also common — if you see ice anywhere on the system, turn it off and let it thaw for 24 hours before restarting.

On the safety side, a system running constantly drives up your hydro bill significantly and puts serious wear on the compressor — the most expensive component to replace. Don't ignore this for more than a day or two.

Your next step is to replace the filter, check your vents, and look for any ice on the unit. If the problem persists after those checks, it's time for a professional diagnostic. A refrigerant leak or dirty coil diagnosis typically runs $200–$400 in the Ottawa market, and a refrigerant recharge is $200–$400 on top of that. For a free estimate or to book a diagnostic visit, reach out to Ottawa HVAC Pro — we service all of Ottawa and the surrounding area.