I’m looking for some advice on a strange issue with my approximately 30-year-old central HVAC system. When I lower the thermostat by 1–2 degrees, the air conditioner will run continuously for a very long time before it finally reaches the new set temperature. For example, if I change the thermostat from 76°F to 75°F, it may eventually reach 75°F, but the AC keeps running even after the thermostat shows it has reached the set point. I’ve also noticed that the house feels much colder than the thermostat setting while it’s still running. The really confusing part is this: if I then raise the thermostat back up to 76°F, the AC immediately shuts off—even though the thermostat may now show the room temperature is 73°F. That doesn’t seem to make sense to me. Has anyone experienced something similar? What are the most likely things I should check or have inspected? Could this be a thermostat issue, a sensor problem, an airflow issue, or something else? The system is about 30 years old, but it still cools the house. I’m just trying to understand why it seems to overcool and why it won’t shut off until I manually increase the thermostat setting. Any advice or troubleshooting suggestions would be greatly appreciated. Thank you!

I wanted to share a DIY HVAC success story from our home in Central Florida. We have a 1,775-square-foot house with a 3-ton, single-stage Bryant system. For a long time, the house never seemed to perform as well as it should. The AC would run short cycles, humidity was inconsistent, some rooms were uncomfortable, and the system seemed to struggle even though it was technically cooling. Instead of immediately replacing the equipment, I started collecting data. I installed an Ecobee thermostat and placed multiple temperature and humidity sensors throughout the house, including the bathrooms, bedrooms, living areas, garage, and attic. I also used a thermal camera, an anemometer, a manometer, and temperature probes to start identifying where the house and duct system were losing performance. Here is what we found: • Several supply registers and return grilles were leaking air around the drywall openings. • The fireplace chase was open to the attic and allowing hot, humid attic air into the conditioned space. • Bathroom exhaust ducts and exterior terminations had damper and sealing issues. • The kitchen range hood had been running continuously and was depressurizing the house. • Some attic insulation had been disturbed or compressed. • The AC blower speed had a major effect on both temperature control and humidity. • The garage door, wall penetrations, and other envelope areas also needed attention. We sealed the supply and return openings, sealed the fireplace chase from above and below, corrected the bathroom exhaust venting, installed proper exterior dampers, sealed penetrations, and stopped running the range hood continuously. We also tested different blower settings instead of assuming the highest airflow was automatically best. The results have been significant. The house now feels noticeably colder and more comfortable at the same thermostat setting. The AC cycles are more stable, room-to-room temperatures are more consistent, and the humidity is under better control. We are comfortable around 72°F without needing a separate whole-house dehumidifier.