This page walks through checks a homeowner can safely make, what each result may point to, and which situations call for stopping the do-it-yourself process immediately.
Start with the safe checks
- 1Confirm the thermostat is in COOL mode, the setpoint is below room temperature, and batteries are fresh.
- 2Look at the filter. If light does not pass through it, replace it before anything else.
- 3Go outside: is the condenser fan spinning and is the unit humming? Note which.
- 4Feel the air at a supply register. Weak air points to airflow; strong but warm air points to refrigerant or the compressor.
- 5Check the breaker panel and the outdoor disconnect for a tripped breaker or pulled fuse, using only a visual check.
- 6Check the drain pan and float switch if accessible — a full pan shuts many systems down completely.
- 7Look for ice on the refrigerant lines or indoor coil. If present, shut cooling off and run the fan.
What each symptom may point to
- Strong airflow, warm air: low refrigerant charge, failed compressor, or the outdoor unit not running
- Weak airflow, cold air: dirty filter, dirty coil, blower problem, duct restriction, or a partially frozen coil
- Nothing runs at all: breaker, float switch, transformer, thermostat, or control board
- Outdoor unit hums but the fan does not spin: failed capacitor or seized fan motor
- System runs constantly and never reaches setpoint: undersized or overloaded system, charge problem, or heavy duct leakage
- Cools at night but not in the afternoon: marginal capacity, dirty condenser coil, or heavy attic heat gain
Brownsville-specific contributing factors
During a Valley heat wave, an air conditioner that is undersized, or one with a coil coated in salt film and dust, may keep up in the morning and fall behind by afternoon. Attic duct systems in attics that can become extremely hot may lose real capacity through leakage and conduction. Homes with large west-facing glass see afternoon loads that no thermostat setting can outrun. Sometimes the equipment is genuinely fine, and the fix is in the ducts, insulation or shading rather than in the condenser.
When to stop and call
- Burning smells, sparking, or a breaker that trips a second time
- Ice on the system that returns after thawing
- Water leaking near electrical components
- Loud mechanical noise from the outdoor unit
- Indoor temperature climbing past the mid-80s with vulnerable occupants at home