How a Home AC System Works

The blower pulls warm indoor air through the return grille and filter, then pushes it across the evaporator coil. Cold refrigerant inside the coil absorbs heat from that air, and the cooled air continues through the supply ducts to the rooms.

Because the coil is colder than the dew point of the indoor air, moisture condenses on it. That water drips into the drain pan and leaves through the condensate line — a significant volume during Georgia summers.

The compressor raises the refrigerant's pressure and temperature so it becomes hotter than the outdoor air. The condenser coil then releases that heat while the outdoor fan pulls air across it.

This is why a dirty outdoor coil hurts so much: if heat cannot leave the refrigerant outdoors, it cannot be absorbed indoors either.

After shedding heat, the liquid refrigerant passes through a metering device that drops its pressure sharply. That pressure drop makes it cold again before it returns to the indoor coil, and the cycle continues.

The refrigerant cycle only works if enough air passes across both coils. Restrict indoor airflow and the coil gets too cold and freezes. Restrict outdoor airflow and pressures climb, capacity drops, and the compressor works harder than it should.

A heat pump adds a reversing valve, allowing refrigerant flow to switch direction so the outdoor coil absorbs heat and the indoor coil releases it. That is why heat pumps dominate in mild-winter climates like Columbus.