Your HVAC
Parts of an air conditioner
Learn what the outdoor unit, indoor coil, blower, refrigerant lines, thermostat, and ducts each do.
Every central AC has an outdoor compressor, condenser coil, and fan; an indoor evaporator coil and blower; refrigerant lines; controls; and ducts. Knowing each part’s job helps you describe the symptom without guessing which part failed.
Outdoor unit: compressor, condenser coil, and fan
The outdoor cabinet houses the compressor, condenser coil, and fan. Check that leaves and stored items are not blocking airflow and note visible cabinet damage. Keep the cabinet closed; it contains energized components, including a capacitor that can retain charge.
Indoor unit: evaporator coil and blower
Inside the home, the evaporator coil absorbs heat from indoor air as refrigerant passes through it, while the blower (part of the air handler or furnace cabinet) pushes air across that coil and through the ducts. You can observe whether the blower sounds unusually loud or whether airflow from vents feels weak, but diagnosing a dirty or icing evaporator coil, or adjusting blower settings, is equipment testing.
Refrigerant lines and charge
Two copper lines circulate refrigerant between the indoor and outdoor units. Charge has to match manufacturer specifications; an incorrect charge raises energy use and failure risk. ENERGY STAR includes charge verification in a quality installation (ENERGY STAR).
Thermostat and controls
The thermostat senses temperature and signals the system to start or stop. Check the mode, setpoint, schedule, active sensor, and batteries before assuming the equipment ignored a cooling call.
Ductwork and airflow
Ducts carry conditioned air to each room and return air to the blower. Leaks, restrictions, poor sizing, and missing return paths waste energy and create uneven rooms. A leakage test and airflow readings show whether the delivery system meets the equipment’s needs (ENERGY STAR).
Sizing: why bigger isn’t better
An air conditioner that’s the wrong size for your home can cycle too frequently, leading to poor comfort and a shorter equipment lifespan. Proper sizing depends on your home’s actual characteristics rather than a simple rule of thumb, so ask any contractor how they calculated the sizing for your specific house (ENERGY STAR).
For broader guidance on home cooling systems, see the HVAC section.
Sources
- Department of Energy, accessed 8/12/2026
- HVAC Quality Installation | ENERGY STAR, accessed 8/12/2026