Compressor: how the AC compressor works in Dunwoody 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 Dunwoody homes

Older duct systems in this area often leak 20–30% of their air into attics and crawlspaces during peak summer. In Dunwoody's mix of 1970s and 1980s traditional homes, many with original duct runs and second-generation equipment, we see compressor issues most often in homes around Dunwoody Village, Georgetown, Kingsley.

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.