How a central air system works

Transcript

1. How a central air system works

   A split-system air conditioner moves heat; it doesn’t make cold. In ten short chapters, here is the path the air and the refrigerant take through a typical North Texas home.

2. The thermostat calls for cooling

   When indoor temperature rises above the setpoint, the thermostat closes a low-voltage circuit that starts the outdoor compressor and condenser fan, and the indoor blower.

3. Return air is drawn in

   The blower creates negative pressure on the return side, pulling room air through the return grille and return duct, along with the dust, dander and pollen suspended in it.

4. Filtration

   Before the air reaches the coil, it passes the filter. EPA recommends at least MERV 13 where the system allows; that rating captures at least half of particles 0.3 to 1 micron, protecting the occupants and the coil.

5. Heat and moisture removal at the evaporator coil

   Inside the coil, low-pressure refrigerant boils and absorbs heat from the air crossing the fins. Air typically leaves 15–20 °F cooler, and water vapor condenses on the cold surface: that is how the system dehumidifies.

6. Condensate drainage

   The water collects in the drain pan and leaves through the condensate line. A clogged line is the most common cause of summer leaks and float-switch shutdowns, and a constantly wet coil is where biofilm forms.

7. Distribution

   The blower delivers conditioned air through the supply plenum, trunk and branch ducts to every register. Leaky joints, crushed flex runs or a fouled blower wheel reduce what actually reaches each room.

8. Heat rejection outdoors

   Now a low-pressure vapor carrying the home’s heat, the refrigerant travels through the insulated suction line to the compressor. Compression raises its pressure and temperature so the condenser coil and fan can release that heat outdoors.

9. Metering, and the cycle repeats

   Condensed to a high-pressure liquid, the refrigerant returns through the liquid line to the metering device at the indoor coil. Its pressure drops sharply, it turns cold again, and the cycle continues until the setpoint is met.

10. Where performance is lost

    Every stage depends on clean surfaces and open airflow. A loaded filter, a fouled coil or blower wheel, or a blocked drain each cut capacity and raise indoor humidity. That is why we restore the whole system, not just the vents.