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- Heat-wave check
Is it broken, or is it just 106 outside?
On the hottest afternoons a healthy system can sit a few degrees above the set point. Knowing which side of that line you are on is worth a phone call either way.
The check
Three numbers and one question. It runs in your browser and nothing is sent anywhere. It is a guide to whether the gap you are seeing is normal for the weather — it cannot tell you what has failed.
What this looks like
Nothing is running outside
Before anything else, three things stop a system that is otherwise healthy.
- The breaker for the outdoor unit, and the one for the indoor unit
- The service switch on the wall beside the outdoor unit and beside the furnace or air handler
- The float switch on the condensate drain, which cuts cooling when the pan fills
If all three are fine and it still will not start, it needs a visit.
This is a system doing its job
You are at or near the set point in this weather, which is what a healthy system looks like.
- Keep the filter clean — it is the cheapest way to protect this
- Keep the outdoor coil clear of dust, cottonwood and stacked items
- Nothing here needs a call-out
A few degrees behind, on a very hot day
Sitting a little above the set point when it is this hot outside is normal. Equipment is sized for a design temperature, and on the worst afternoons of the year it runs continuously and still loses a few degrees.
- Check the filter and rinse the outdoor coil gently from the inside out
- Close blinds on the sun side during the afternoon
- If the same gap appears on a mild day, that is when to call
Losing ground earlier than it should
At this outdoor temperature a healthy system should be holding the set point. A gap this size points at something measurable rather than at the weather.
- Common causes: a loaded filter, a dirty coil, low refrigerant charge or leaking ducts
- Change the filter and look at the outdoor coil first — both are free to check
- If that does not close the gap, book a visit while it is still a small fault
Well short of the set point
A gap this wide is more than the weather, even in a heat wave. The system is running but it is not moving enough heat out of the building.
- Check the filter, the outdoor coil and the condensate drain
- Feel the large copper line at the outdoor unit — if it is not cold and sweating, mention that when you call
- This one is worth booking rather than waiting out
Something has failed
At this outdoor temperature the indoor reading should not be this far from the set point. This is a fault, not the weather.
- Switch the cooling off if you see ice on the pipework or water around the indoor unit
- Note anything that changed — a noise, a breaker, a smell
- Call and describe those; it decides what we bring
Four things that decide a hot afternoon
- Design temperatureEquipment is sized to hold a comfortable indoor temperature at a chosen outdoor design figure. Above that, everything runs continuously and still drifts. That is arithmetic, not a defect.
- Coil conditionA condenser coil packed with dust cannot reject heat. It is the single most common reason a system that was fine in June struggles in late July.
- Duct lossesDucts in a very hot attic lose cooling on the way to the room, and a leaking return pulls attic air into the system. Both look exactly like an undersized system.
- Sun and glassWest-facing glass on a 105°F afternoon adds load faster than most systems can remove it. Shading it is cheaper than upsizing anything.
