If your AC is working but your home still feels warm and sticky, you’re not imagining it.
When the St. Louis heat sets in, there’s nothing more frustrating than an air conditioner that’s clearly running — you can hear it, you can feel air moving — but the house just won’t cool down. If your AC is working but your home still feels warm and sticky, you’re not imagining it, and you’re not alone. This is one of the most common summer calls we get from homeowners across the St. Louis metro.
First, the easy things to check yourself
Before assuming the worst, run through these quick checks. More often than you’d think, the fix is something minor.
- Check your thermostat settings. Make sure it’s set to “cool” and not just “fan.” If the fan is set to “on,” air will blow constantly whether or not it’s being cooled — which can make it feel like the system is running while the house stays warm. Switch the fan to “auto” and set the temperature a few degrees below the current room temperature.
- Look at your air filter. A clogged filter is the single most common reason a working AC can’t keep up. When the filter is packed with dust and debris, airflow drops, cooling suffers, and the whole system strains. If you can’t remember the last time you changed it, that’s a strong sign. Pull it out and hold it up to the light — if you can’t see through it, replace it.
- Check your vents and registers. Make sure supply vents throughout the house are open and not blocked by furniture, rugs, or curtains. Closing too many vents can throw off the system’s balance and reduce overall cooling.
- Look outside at the condenser unit. That’s the large outdoor unit. Make sure it isn’t buried in grass clippings, leaves, or debris, and that there’s clear space around it. The outdoor unit releases the heat your AC pulls out of your home, and if it can’t breathe, it can’t cool.
If you’ve checked all of these and the house still won’t cool, the problem likely needs a closer look.
Common reasons your AC runs but won’t cool
When the basics check out, here are the issues we most often find on St. Louis service calls.
- Low refrigerant or a refrigerant leak – Refrigerant is what your AC uses to actually remove heat from your home. If the level is low — almost always because of a leak — the system will run continuously but never reach the set temperature. You may notice the air from the vents isn’t very cold, or that cooling is much weaker than it used to be. Refrigerant issues aren’t a DIY fix; they require a licensed technician to locate the leak, repair it, and properly recharge the system.
- A frozen evaporator coil – If your indoor coil ices over, your AC can run without cooling the house at all. Ironically, a frozen coil often comes from restricted airflow (a dirty filter) or low refrigerant. Signs include weak airflow, ice visible on the unit or refrigerant lines, and water pooling around the indoor unit as the ice melts. If you suspect a frozen coil, turn the system off to let it thaw, then call a professional — running it while frozen can cause further damage.
- Dirty condenser coils – Over a St. Louis summer, the outdoor unit collects dust, pollen, and grime. When the condenser coils get coated, the system can’t release heat efficiently, so it runs and runs without bringing the indoor temperature down. A professional cleaning usually restores performance.
- A failing compressor or capacitor – The compressor is the heart of your cooling system, and the capacitor helps start and run key components. When either begins to fail, the system may fail to cool effectively. These are mechanical problems that need to be diagnosed and repaired by a technician.
- Your system is undersized or aging – If your AC has never quite kept up on the hottest days, it may be undersized for your home. And if it’s more than 10 to 15 years old, declining performance is common — older systems lose efficiency and struggle against St. Louis humidity. In these cases, repair may be a short-term fix, and it’s worth talking through whether replacement makes more sense.
When to call a professional
Call an HVAC technician if:
- The air from your vents isn’t cold, even with a clean filter
- You see ice on the unit or refrigerant lines
- The system runs constantly, but never reaches the set temperature
- You hear unusual noises, or the unit is short-cycling on and off
- Cooling has gotten noticeably weaker over time
In the middle of a St. Louis summer, a struggling AC can turn into a no-cooling emergency fast — especially for homes with young children, older adults, or anyone sensitive to heat. There’s no need to tough it out.
What to expect when you call us
When you reach out to Thomas Hoffmann Air Conditioning & Heating, here’s how we handle it. We’ll get details about what your system is doing, schedule a visit that works for you, and send a technician to diagnose the actual cause — not just guess at it. We’ll explain what we find in plain terms, walk you through your options, and give you a clear path forward. No pressure, no corporate runaround.
As a locally owned St. Louis HVAC company, we treat our neighbors the way we’d want to be treated. That’s a real difference from the national chains that operate under local-sounding names but answer to corporate.