AC Won't Turn On in Markham? Try These Steps Before Calling for Repair

Most newer installs — very common in Markham and Richmond Hill's finished basements — have a condensate overflow switch that shuts the whole system down if the drain pan or line backs up. It's a safety feature protecting your ceiling and floors, not a malfunction. Look at the drain pan under the indoor unit; if it's full or the float switch has tripped, clear the line before assuming compressor failure.

Central air typically draws from a dedicated breaker at both the main panel and a disconnect box next to the outdoor unit. Check both — the outdoor disconnect gets bumped or left open more often than people expect, especially after landscaping or deck work.

Confirm it's set to cool, not just "on" fan mode, and that the set temperature is a few degrees below room temperature. Smart thermostats with scheduling can silently revert to a heat mode after a power blip — worth ruling out before anything else.

If the outdoor unit is running but the house isn't cooling, a filthy filter or a frozen indoor coil (visible ice on the lines) is often the real issue — both restrict airflow and can shut the system down on a safety limit. Turn the system off, let a frozen coil thaw fully, replace the filter, then try again before booking anything.

If the outdoor unit hums but the fan doesn't spin, that's often a failed run capacitor — a fast, inexpensive fix when caught early, and a burned-out compressor when ignored too long. That distinction is worth a proper diagnosis rather than a guess, especially heading into a July weekend in Markham when everyone else's AC is also failing and scheduling gets tight.