How Your AC System Actually Works
Most people run their AC every day without knowing what’s inside it — until something breaks. This guide gives you a clear picture of every component, how they connect, and what warning signs to watch for.
Inside Your Split-System AC
A central AC has two units — outdoor and indoor — working in sync. Click any numbered part on the diagram (or the legend below) to see what it does and what to watch for.
Click a numbered component on the diagram to learn what it does.
The 4 Stages of the Refrigeration Cycle
Your AC doesn’t generate cold air — it moves heat from inside your home to outside. It does this by cycling refrigerant through 4 stages, continuously, every time the system runs.
Compression
The cycle begins here. The compressor pulls in refrigerant as a cool, low-pressure gas and squeezes it under intense mechanical force — think of pumping up a bicycle tire. This compression raises both the pressure and temperature dramatically. The refrigerant exits as a superheated gas ready to dump heat outside.
- Refrigerant enters cool and low-pressure
- Pressure rises to 200–400 PSI
- Temperature jumps to 100–120°F
- Most electricity-intensive stage of the cycle
Condensation
The hot, pressurized gas flows through the condenser coil — the copper tubing wrapped around the inside of your outdoor unit. The condenser fan pulls outside air across these coils. Heat transfers from the hot refrigerant into the outdoor air (you can feel this heat blowing out the top of the unit). As the refrigerant loses heat, it cools and changes state from gas to liquid.
- Hot gas flows through serpentine copper coils
- Condenser fan pulls outdoor air across the coil
- Heat from your home is released outside
- Refrigerant condenses into a warm liquid
Expansion
The warm liquid refrigerant travels indoors via the liquid line and passes through the expansion valve (TXV) — a small precision metering device with a tiny orifice. As the liquid passes through it, the pressure drops suddenly and dramatically. This rapid pressure drop causes the refrigerant to become a cold, partially-vaporized mist — ready to absorb heat inside your home.
- Refrigerant passes through a tiny precision orifice
- Pressure drops from ~250 PSI to ~70 PSI
- Temperature plummets from ~100°F to ~40°F
- Refrigerant becomes a cold liquid-vapor mist
Evaporation
The cold refrigerant mist flows through the evaporator coil inside your air handler. Your blower fan pushes warm household air across these frigid coils. The refrigerant absorbs the heat from that air and evaporates back into a gas. The air, now cooled and dehumidified, is pushed through your ductwork and into your rooms. The refrigerant gas travels back to the compressor and the entire cycle repeats — continuously — until your thermostat is satisfied.
- Cold refrigerant flows through the evaporator coil
- Blower pushes warm room air across the coils
- Refrigerant absorbs heat and evaporates to gas
- Cooled, dehumidified air flows into your home
- Gas returns to compressor — cycle repeats
What to Watch For in Each Stage
Now that you understand the cycle, here are the most common failure symptoms Central Florida and Tampa homeowners see — and which component is usually to blame.
Unit Won’t Start / Just Hums
Often a failed capacitor. The compressor or fan motor is trying to start but can’t get the initial electrical kick it needs. Usually a $150–$350 fix.
System Runs But Doesn’t Cool
Low refrigerant (leak), failed compressor, or dirty condenser coil. If you see ice on the suction line, turn it off and call us.
Weak Airflow From Vents
Usually a clogged air filter, failing blower motor, or frozen evaporator coil from restricted airflow. Check your filter first — it’s free.
Water Near the Indoor Unit
Clogged condensate drain line — extremely common in Florida. The drain pan overflows. A quarterly flush with diluted bleach prevents most of these calls.
High Electric Bills
Dirty condenser coil, low refrigerant, or a failing compressor forces the system to work harder and run longer to achieve the same cooling. Annual maintenance catches these early.
Musty or Mildewy Smell
Mold or mildew growing on the evaporator coil or in the drain pan. Common in Florida due to humidity. A coil cleaning and drain treatment clears it up.
Know your system. Trust your technician.
Al-Air’s licensed HVAC technicians service every component covered on this page — from capacitor swaps to full system replacements. 14+ years serving Central Florida and Tampa.
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