73 Degrees. That Is What the Thermostat Says. So Why Does It Feel Like 80?
You set your thermostat. You wait. The AC kicks on and runs and runs. But the temperature reading barely moves, and walking through your living room still feels like stepping into a slow oven.
When your thermostat is not reaching the set temperature, most people’s first instinct is to blame the thermostat itself. Sometimes that is right. But in most of the cases we see at All Star Heating & Cooling, the thermostat is just the messenger. The actual problem is somewhere in the HVAC system.
Let us work through what is actually happening and how to figure out which category your situation falls into.
Start Here: The Thermostat Itself
Fair enough, let us rule it out first.
Thermostats can malfunction in a few specific ways that make them inaccurate. If the thermostat is located in a spot that gets direct sunlight, sits near a heat-producing appliance, or is positioned on an exterior wall with poor insulation, it may be reading the local temperature around the device rather than your home’s actual ambient temperature. The thermostat thinks the house is cooler than it is, stops calling for cooling prematurely, and the rest of your home stays warm.
Low batteries can cause erratic behavior in some smart and programmable thermostats. Strange temperature readings, delayed responses, and failure to hold settings are all possible symptoms. This is the easiest fix on this entire list, so swap the batteries before you do anything else.
If your thermostat is more than ten years old and particularly if it is an older non-programmable model, calibration drift is a real possibility. Older bimetallic thermostats can become inaccurate over time. A simple test: place a reliable thermometer next to your thermostat and compare the readings. If they are off by more than a degree or two, the thermostat itself may need replacement.
Modern programmable and smart thermostats are relatively inexpensive and can make a real difference. But again, replacing the thermostat when the underlying issue is the AC system will not solve anything.
The AC Is Running but Falling Behind
This is the more common scenario we find. The thermostat is working correctly. It is calling for cooling. The AC responds and runs. But the system simply cannot produce enough cold air to bring the home down to the target temperature.
There are several reasons this happens, and they tend to get more pronounced in Central Florida during peak summer.
The system is undersized for the heat load. This is probably the most underappreciated cause of this problem. An AC system that was correctly sized for your home ten years ago may not be adequate today if you have added square footage, replaced single-pane windows with large glass panes, or even just if the insulation in your attic has degraded. On a day when temperatures are above 90 degrees, an undersized system will run continuously and still fall short of your set temperature. It is not broken. It is just outmatched.
Refrigerant is low. A system running low on refrigerant loses its ability to absorb heat effectively. The AC runs and runs, but because the refrigerant charge is insufficient, the amount of heat it can remove from your home per hour drops. We wrote about refrigerant leaks in detail in our post on AC refrigerant leak repair in Central Florida if you want to dig into that topic further. The key takeaway: low refrigerant always traces back to a leak that needs to be repaired, not just topped off.
Dirty coils. Your evaporator coil, the indoor one, and your condenser coil, the outdoor one, are both heat exchange surfaces. When they are coated in dirt and dust, they cannot exchange heat as efficiently. A dirty evaporator coil cannot absorb as much heat from your indoor air. A dirty condenser coil cannot release that heat into the outdoor air. Both problems limit your system’s effective output.
Airflow Problems Can Fool You
Here is a situation that genuinely tricks people. The AC is producing cold air. Plenty of it. But it is not getting to where it needs to go.
Leaky or poorly designed ductwork is a significant problem in many Central Florida homes, especially those built in the 1970s through 1990s. If conditioned air is leaking out of your ducts into your attic before it reaches your living spaces, your thermostat will keep calling for cooling because the rooms never get cold enough. The AC keeps running. Your electric bill keeps climbing. And you keep adjusting the thermostat downward, which does not actually solve the problem.
A related issue is blocked or closed supply vents. Closing vents in unused rooms feels intuitive as an energy-saving measure. But modern duct systems are designed around a specific airflow balance. Closing vents in some rooms creates backpressure in the duct system, reduces airflow elsewhere, and can actually cause your system to work less efficiently overall. According to the Department of Energy, duct leakage accounts for significant energy waste in many American homes, and the impact on comfort is real.
When the Problem Is the Home, Not the System
Sometimes I walk through a customer’s home and the AC is genuinely doing everything it can. The system is properly sized, refrigerant is good, coils are clean, ducts are intact. And the house still cannot get below 76 degrees on a hot day.
In those cases, the building envelope is usually the issue. Poor attic insulation is the most common culprit in Florida. Heat radiates through your roof and into the attic, and if the attic insulation is thin or degraded, that heat conducts into your living space faster than your AC can remove it. Adding attic insulation is one of the highest-return home improvements you can make in Central Florida.
Air sealing is the other big one. Gaps around recessed lights, plumbing penetrations, attic hatches, and door frames let conditioned air escape and hot air creep in. The Energy Star program has clear guidance on air sealing that is worth reviewing if you think your home’s envelope might be contributing to the problem.
We can tell you honestly whether the issue seems HVAC-related or building-related when we are on site. We would rather point you in the right direction than sell you a service you do not need.
Getting Your Home to the Temperature You Set
A thermostat not reaching the set temperature is worth taking seriously. It is your system telling you something is off, and ignoring it usually means higher electric bills, more wear on your equipment, and a home that stays uncomfortable through the worst months of a Central Florida summer.
Work through the basics first: fresh batteries, check that vents are open and unblocked, look at whether the thermostat is in a good location. But if none of that points to an obvious fix, please reach out to our team at All Star Heating & Cooling. We will come out, run a proper diagnostic, and give you a clear answer on what is keeping your home from reaching that set temperature. Just give us a call and we will take care of you.