(830) 555-0142

AC Not Cooling? A Quick Diagnostic Checklist

A practical homeowner checklist for New Braunfels heat. Five things to check yourself before calling, and when it's time to dial.

Quick answer

Five-step homeowner check: (1) verify the thermostat is set to COOL and the temperature is below current room temp, (2) change the air filter, (3) check the breaker for the AC at the panel, (4) look for ice on the indoor evaporator coil (in the air handler closet or attic), and (5) walk outside and verify the condenser unit is running and the fan is spinning. If all five are fine and the AC still won't cool, it's a refrigerant, capacitor, or compressor issue — call a technician.

Step-by-step

  1. Thermostat check. Set to COOL, fan to AUTO (not ON), and the target temperature 3-5 degrees below current room temperature. If you have a smart thermostat that recently updated, verify the cooling schedule wasn't changed.
  2. Filter check. Pull the filter from the return-air grille or the air handler. If you can't see light through it, change it. A clogged filter is the #1 cause of AC underperformance in New Braunfels — and it can lead to a frozen coil that takes the system offline entirely.
  3. Breaker check. Open your electrical panel. Find the breaker labeled AC or HVAC (usually a double-pole 30-50A breaker). If it's tripped (sitting between ON and OFF), flip fully OFF, wait 30 seconds, then flip back to ON. If it trips again immediately, stop and call — that's an electrical short and not safe to keep resetting.
  4. Frozen coil check. Open the air handler closet (usually in a hallway, garage, or attic). Look for ice or frost on the copper tubing going into the evaporator coil. If you see ice, the coil is frozen — usually from a dirty filter that's been ignored too long. Turn the system OFF at the thermostat, run just the fan for 2-3 hours to thaw, then restart on COOL.
  5. Outdoor unit check. Walk outside to the condenser unit. With the system calling for cool, the fan on top of the unit should be spinning and you should hear a low compressor hum. If the fan isn't spinning but you hear humming, the run capacitor has failed — common Texas summer repair, cheap part, call a technician.

When to call

If all five checks pass and the AC still won't cool, it's one of three things: low refrigerant (slow leak somewhere in the system), failed capacitor or contactor at the outdoor unit, or failed compressor (worst case, often a replace-the-unit conversation). All three require a licensed HVAC technician with EPA-certified refrigerant gauges. AC repair handles all three.

What NOT to do

  • Don't keep resetting a tripping breaker. That's an electrical fault — keep resetting and you can damage the unit or start a fire.
  • Don't add refrigerant yourself. R-410A and R-22 require EPA certification to purchase or handle. DIY refrigerant from auto-parts stores is the wrong product and can damage the system.
  • Don't ignore a frozen coil. Running the AC with ice on the coil blows the blower motor and can crack the coil itself. Always thaw first.
  • Don't bypass the thermostat. The control circuit is doing safety work. Bypassing it can cause the compressor to short-cycle and burn out.

Need an HVAC technician? (830) 555-0142. 24/7 emergency dispatch for cooling failures during summer heat.