Why your AC quits on the hottest weekend of the year

Every summer we take the same calls on the same weekends. Fourth of July, Memorial Day, the first stretch of days over ninety five. People figure it's bad luck.

It isn't. There's a mechanism behind it, and once you see it you can usually stop it happening to you.

What's going on

An air conditioner doesn't fail because it's hot outside. It fails because heat removes the margin that was hiding a problem you already had.

A capacitor that's weak but working will start the compressor fine on an eighty degree day. On a ninety eight degree day, with the unit running almost continuously and the head pressure high, that same capacitor can't deliver enough of a kick. The compressor tries, draws too much current, and the overload trips. To you it looks sudden. It wasn't.

Same story with a condenser packed with cottonwood and grass clippings, a low refrigerant charge from a slow leak, or a contactor with pitted points. All three are survivable in mild weather. None of them survive a heat wave.

Why the Lake makes it worse

Two things stack here that don't stack everywhere. Holiday weekends mean a lot of houses that have been sitting empty suddenly get occupied, thermostats get set to sixty eight, and equipment that hasn't run in weeks is asked to run flat out. And everybody on the water is doing it at the same time, which is also when every HVAC company in the county is at capacity.

That's why we answer the phone at two in the morning.

Three things that prevent most of it

• Replace the capacitor before it fails. It's one of the cheapest parts in the system and the single most common cause of a summer no cool call. If yours is more than about eight years old, replacing it early costs very little.
• Clean the condenser coil properly. Not a quick spray from the top. The debris that matters is packed down into the fins, and around here that means cottonwood, grass and lake dust. A restricted coil raises head pressure, which is exactly the condition that kills marginal parts.
• Get the charge checked once a season. A system low on refrigerant is leaking. Topping it up without finding the leak gets more expensive every year, so ask for the leak to be found, not just the pressure corrected.

If it already quit

Turn the thermostat to off rather than leaving it calling for cool. A compressor that keeps trying to start against an overload is a compressor you're actively damaging, and the compressor is the expensive part.

Then call us. Around the clock, every day of the year, holiday weekends included.