Compressor: how the AC compressor works in Alpharetta homes

The compressor is the pump in the outdoor unit that moves refrigerant through the whole system. It squeezes low-pressure vapor from the evaporator coil into hot, high-pressure gas so it can release heat outdoors.

How it works

Most modern home systems use a sealed scroll compressor — the black or gray dome inside the outdoor cabinet. Two spiral scrolls compress the refrigerant as one orbits against the other.

The compressor gets its start from a capacitor and a contactor controlled by your thermostat. Hard starts, high head pressure from a dirty coil and low refrigerant all shorten its life.

Single-stage compressors run at full speed or off. Two-stage and variable-speed (inverter) compressors run longer at lower speed, which removes more humidity and is quieter — a real advantage in Atlanta summers.

Signs of a problem

Clicking on and off repeatedly
Outdoor unit runs but air inside isn't cold
Loud buzz or bang at startup
Breaker trips when cooling starts
Higher power bills with less comfort

Simple upkeep

Keep the outdoor coil clean so head pressure stays normal
Fix fan and capacitor problems right away
Don't restart the system immediately after a power outage — wait 5 minutes
Get refrigerant leaks repaired, not just topped off

The compressor in Alpharetta homes

Large homes with zoned systems run long cooling cycles; mismatched zones show up as one floor staying warm all summer. In Alpharetta's mix of two-story subdivisions from the 1990s and 2000s, often with two or three zoned systems and a basement furnace, we see compressor issues most often in homes around Downtown Alpharetta, Windward, Crabapple.

What our technicians check: When a compressor won't start, we check the capacitor, contactor and windings before calling it failed. Many 'dead compressors' are actually a $20-class electrical part that failed first.