Start Here: Is the System Actually Running?
Before diagnosing a cooling problem, confirm both the indoor air handler and the outdoor condenser unit are running. A system where only the air handler runs — but the compressor outside is silent — has a specific set of causes different from one where nothing is running at all.
1. Dirty or Clogged Air Filter
A clogged filter is the most common cause of reduced cooling and the easiest to fix. When the filter is blocked, airflow across the evaporator coil drops — the coil freezes, and the system loses its ability to remove heat from your home. Check your filter first. If it's gray and you can't see through it, replace it. Filters in the Hill Country often need replacement every 4–6 weeks during cedar season.
2. Frozen Evaporator Coil
A frozen coil feels counterintuitive — ice on the coil means the system can't cool your home. Causes include: a clogged filter (see above), low refrigerant, or a blower motor issue. If you see ice on the indoor unit or copper lines, turn the system off and let it thaw for 2–4 hours. If it refreezes, call a technician — you likely have a refrigerant or airflow problem.
3. Low or Leaking Refrigerant
Refrigerant is not "used up" like fuel — if your system is low, there's a leak somewhere. Low refrigerant means the system can't absorb heat efficiently. Signs include: ice on the coil or lines, a hissing or bubbling sound, or significantly warmer air than usual from vents. Refrigerant work requires a licensed HVAC technician — it's not a DIY repair.
4. Dirty Condenser Coils (Outdoor Unit)
The outdoor condenser unit releases the heat your AC pulls from inside your home. If the coils are coated in dirt, grass clippings, or cottonwood seeds, the system can't release heat efficiently. Keep at least 2 feet of clearance around the outdoor unit and gently rinse the coils with a garden hose annually. Don't use a pressure washer — it can bend the fins.
5. Failed Capacitor
Capacitors are small cylindrical components that give the compressor and fan motors the jolt they need to start. A failed capacitor is one of the most common AC repair calls in Texas — especially after a summer of heavy use. Symptoms include: the outdoor unit humming but not spinning, or the system clicking on and off repeatedly. Capacitor replacement is a quick, affordable fix for a licensed technician.
6. Thermostat Issues
Before assuming a mechanical failure, check your thermostat. Common issues: batteries are dead, it's set to "fan only" instead of "cool," or it's been bumped to a higher set point. If you have a smart thermostat, check whether it's in schedule mode and suppressing cooling during certain hours.
7. Undersized System or Duct Leaks
If your AC runs constantly but the house never reaches the set temperature, the system may be undersized for your square footage — especially if you've added rooms or converted a garage. Duct leaks can also cause 20–30% of conditioned air to escape into the attic before reaching your living space. Both issues require a professional assessment.
When to Call O2 Kool
If you've checked the filter, confirmed the thermostat settings, and cleared debris from the outdoor unit and the system still isn't cooling — it's time to call. O2 Kool offers same-day diagnostics throughout Kingsland and the Texas Hill Country. We'll identify the cause, give you an honest quote, and fix it right the first time. Call (325) 388-5665 — we're available 24/7.