Cooling

AC Not Cooling the House? Why It Won’t Drop Below 75

Your thermostat says 70, the AC runs all afternoon, and the house won't drop below 75. Here's what we check first, and what you can check before you call.

info@kangomedia.com

September 26, 2026

HVAC technician in a navy uniform checking refrigerant pressures with manifold gauges at an outdoor AC condenser beside a Colorado home, mountains in the distance

The thermostat is set to 70. The AC has been running since lunch on a hot Denver-metro day. And the house is sitting at 75, maybe 76. The air coming out of the vents feels cool, just not cool enough.

Here’s the short version: if you’re asking for 70 and the house never gets below 75 or 76, something is wrong. The good news is that the cause is often simple. The trick is finding it, instead of guessing.

First, is it just the heat?

On the hottest afternoons of the year, even a healthy air conditioner can run nonstop and fall a few degrees behind. If the house catches up in the evening and holds your setting overnight, your system may simply be working hard on a very hot day.

A system that never catches up, even after the sun goes down, is telling you something. So is one that fell behind this summer when it didn’t last summer.

A system that never catches up, even after the sun goes down, is telling you something.

What you can check yourself

Before you call anyone, a few quick checks can save you a service visit:

The thermostat. Make sure it’s set to “Cool” and the fan is on “Auto.” If it runs on batteries, try fresh ones.
The air filter. A clogged filter is one of the most common reasons an AC can’t keep up. If it’s gray and packed with dust, replace it.
Vents and returns. Open the supply vents and make sure nothing is blocking the return grilles, like furniture, rugs, or boxes.
The outdoor unit. Is the fan on top spinning? Clear away weeds, leaves, or anything stacked against it. The unit needs room to breathe.
The breaker. If the outdoor unit isn’t running at all, check the breaker panel.

If all of that looks fine and the house still won’t cool, it’s time for a diagnosis.

The most common causes we find

Restricted airflow. Besides a dirty filter, the problem can be on the return side, the ducts that pull air back to the system. When a return is too small, blocked, or leaking, the system can’t move enough air, and the cooling suffers.
Dirty coils. The outdoor condenser coil gets rid of the heat from your home, and the indoor evaporator coil absorbs it. When either one is coated in dust and grime, the whole system works harder and cools less. Cleaning both is part of a good tune-up.
Low refrigerant from a leak. If the system is low, it’s leaking somewhere. You might see ice on the copper line outside. We explain that one in Why Is the Copper Line on My AC Freezing?
A failing capacitor or relay. These small electrical parts help the motors start and run. When one weakens, the outdoor fan or the compressor may struggle, hum, or stop.
A compressor problem. The compressor is the heart of the system. A failing compressor can trip the breaker again and again.
A system that’s the wrong size. If the AC was never sized for the house, or the house has changed with an addition or a finished basement, it may never keep up on hot days.

How we find the real problem

When we come out, we don’t start with the most expensive part. We start with the small, simple things, like the capacitor, the relay, and the wiring, and work through the system in order. Checking in order matters. A tech who jumps ahead to the part they suspect can replace it and still leave the real problem behind. Going step by step finds the part that actually failed, so you only pay for what the system needs.

Say the breaker keeps tripping. We might check the capacitor and the relay, find them fine, and keep going until we find that the compressor is the reason. At that point it makes sense, and we’ll show you why.

Then we talk options. If it’s a simple repair, you’ll get a clear price. If it’s a major part on an older system, we’ll lay out both paths, repair or replace, with real numbers for each. Some people prefer to fix it; some would rather go new. Either way, it’s your call.