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Why the house won't hold 72° when it's 110° out.
Every air conditioner has limits. On the hottest valley afternoons, a healthy system can run all day and still let the house drift. Here is how to tell normal from a fault.
About twenty degrees, not forty.
A common rule of thumb in the trade is that a correctly sized system in a hot climate can hold the house roughly 20°F below the outdoor temperature at the peak of the day. Systems here are sized for a "design" afternoon of around 100°F — the exact figure comes from the load calculation for your house.
Illustrative only: the indoor figure is the rule of thumb, not a promise for any particular house.
What to expect, and when to call.
Up to about 100°
A healthy, correctly sized system should reach and hold your setting, cycling on and off. If it can't, something is wrong — call us.
About 100° to 107°
Long run times are normal. The house may sit a degree or two above the setting in the late afternoon and catch up in the evening.
Hotter than that
The system may run without stopping and the house may drift several degrees. That alone is not a fault. Warm air from the vents, ice or short cycling is.
Call us if you see any of these.
- Warm air from the ventsThe system runs but the air isn't cool.
- Ice on the pipesTurn cooling off, fan on, and call.
- Short cyclingStarting and stopping every few minutes.
- Outdoor fan not turningWhile the unit hums or the compressor runs.
- Water near the indoor unitA drain backing up.
- Breaker trippingReset once; if it trips again, leave it off.
What you can do today.
- Start earlierLet it cool the house in the morning, rather than catch up at 4pm.
- Close west blindsAfternoon sun on west glass is a big load.
- Don't set 60°A lower setting doesn't cool faster; it just runs longer.
- Change the filterA clogged one cuts airflow on the day you need it most.
At home
Upstairs rooms in two-storey houses run warmest on hot afternoons. Ceiling fans and closed blinds help; if one room is always far warmer, ask us about airflow.
At a business
Doors that open all day and a full shop floor add heat fast. Rooftop units with dirty coils or broken economizer dampers struggle first — plan the spring visit.