Quick answer
- An AC doesn't make cold air — it moves heat out of your house using a refrigerant loop.
- The four key parts are the compressor, condenser coil (outside), evaporator coil (inside), and the metering device.
- The refrigerant changes between gas and liquid four times per cycle to transfer heat.
- Charleston humidity is removed at the indoor coil — every working AC is also a dehumidifier.
- When any of the four components fails, the whole loop stops moving heat.
What 'air conditioning' actually does
An air conditioner doesn't create cold air. It moves heat from inside your house to outside, using a refrigerant loop. That distinction matters because every failure mode is a problem with the heat-moving process, not a problem with 'making cold'.
The same loop, run in reverse, becomes a heat pump — pulling heat from outside air (even when it feels cold out there) and dumping it into your house. That's why heat pumps work so well in Charleston: our winters rarely get cold enough to defeat the loop.
The four components and what each one does
Compressor (outside)
The motor that pressurizes refrigerant gas. It's the most expensive single component in any AC — when it fails on a system over 10 years old, replacement is almost always cheaper than repair.
Condenser coil (outside)
High-pressure refrigerant gas releases its heat to outdoor air here, becoming a liquid. In coastal homes this is the first component salt-air corrosion attacks — fins clog with salt deposits and heat exchange drops.
Evaporator coil (inside)
Low-pressure liquid refrigerant boils into gas here, absorbing heat from your indoor air. This is also where humidity comes out — moisture in your home's air condenses on the cold coil and drips into the drain pan.
Metering device (between the two coils)
Usually a TXV (thermostatic expansion valve) on modern systems. It controls how much refrigerant enters the evaporator coil based on cooling demand. Older systems used a fixed orifice instead; TXVs are more efficient.
Why the same system dehumidifies
Charleston Lowcountry summers hover around 80% outdoor relative humidity. When your AC runs, warm humid indoor air passes over the cold evaporator coil. The air cools and water vapor condenses out — that's the water you see dripping from the condensate drain.
What fails — and what it tells you
- AC not cooling, outdoor unit not running: usually a failed capacitor or contactor — common, inexpensive, often same-day fix.
- AC running but air isn't cold: low refrigerant charge (a leak somewhere in the loop) or a failing compressor.
- Ice on the indoor coil or refrigerant line: airflow problem (dirty filter, blocked return) or low refrigerant.
- Water around the indoor unit: clogged condensate drain — easy fix if caught early, expensive if it overflows into ceilings.
- System runs all the time but won't cool the house: undersized for the load, or duct leakage dumping cold air into the attic.
What to do next
If you know the four components and the cycle, you can have a much more productive conversation with any HVAC contractor. When a tech tells you a part needs replacement, ask which of the four functions it belongs to and what specifically failed in it.
Our team is happy to walk through your system's diagnosis with you — not as a sales pitch, as an explanation. Call us and we'll explain what we're seeing in the same plain language we'd use with a family member.
Have a question about your system?
Talk to a real Charleston Lowcountry technician — a family-owned team with 30+ years of local experience that installs and services Carrier, Trane, Rheem, and more.