AC Running Constantly

[Dwankimoz]

My AC runs constantly but the house still sits around 80 when it's 115 outside. Unit's maybe 8 years old.

Is it time for a new AC unit?

[jackofall]

8 years old shouldn't be struggling that bad on its own, so look at a few things before assuming it's dying.

1. When's the last time the coils were cleaned — desert dust cakes the outdoor condenser coil and kills efficiency, that's the most common thing out here.
2. Check the filter too, same idea, restricted airflow makes the whole system work harder for less.
3. Also worth checking the refrigerant charge if neither of those fixes it — an undercharged system will run nonstop and never quite get there.

115 outside is genuinely hard on any AC, but "running constantly and losing" at only 35 degrees of differential usually means something's reducing its capacity, not that it's just outmatched.

[AshRae]

I thought that you could only expect 20-25 degrees below outside temps? I know insulation and other things play a role but 35 degrees reduction seems pretty good to me.

[hamza1]

At 115°F outside, that's a lot for any AC to handle. I'd start by checking the filters, condenser coils and airflow, just to rule out any issues with the unit itself.

Another thing worth checking is the attic insulation. If the roof is absorbing heat all day, the AC has to work much harder to keep the house cool.

Rigid XPS insulation boards can help reduce heat transfer in suitable roof assemblies. I work with jumbolon, which makes XPS insulation boards, so it's something I'm familiar with. That said, I'd check the existing insulation and ventilation before spending money on upgrades.

Does your AC eventually reach the set temperature at night, or does it struggle even when it's cooler outside?

[seansmith]

AshRae is right that 20 degrees below outside is the usual design target, so holding 80 inside at 115 is actually doing better than spec. That said, if it never shuts off even late at night when it cools down, it is worth a closer look.
A quick check you can do: once it has run for 15 minutes, measure the air temperature at a return grille and at the closest supply vent. A healthy system usually shows about a 15 to 20 degree drop. If you are only seeing 8 to 10 degrees, that points to low refrigerant, a dirty indoor coil, or a weak compressor, and that is when it makes sense to have a tech put gauges on it before deciding to replace the unit.

[dntreecareinc]

At eight years old, I would not jump straight to replacement either. One useful comparison is how the system behaves at night: if it catches up once the outdoor temperature drops, that points more toward heat load, duct losses, or airflow than a unit that has simply worn out. If it still cannot reach the set temperature on a cooler evening, that is a stronger sign something in the system needs attention.

A few checks that have not been covered yet can help narrow it down. Walk the house while it is running and compare airflow at the vents farthest from the air handler with the vents closest to it. A big drop-off can point to a disconnected or crushed duct, a closed damper, or a vent blocked by furniture. Also check that the outdoor unit has clear airflow around it and that the thermostat is not in direct sun or near a heat source, since a warm thermostat reading can keep the system running longer than needed.

If those look normal, having a technician check the system as a whole, including duct condition and refrigerant, makes more sense than replacing based on age alone, especially when the unit still cools well at night.