Sometimes the A/C just doesn’t blow cold air in the summer—or the cooling fades after a few minutes.
It’s hard to tell if a simple refrigerant top-up will fix it, or if core parts like the compressor or condenser need attention.
Knowing the basics—how the system works and what each part does—helps you match symptoms to likely causes and decide on next steps.
How a Car A/C System Works (Quick Basics)
When the engine’s running, the A/C system powers up. Outside air is drawn in and the compressor pressurizes the refrigerant.
- The compressed refrigerant goes to the condenser, where it dumps heat.
- It then passes through the expansion device, where pressure drops.
- The low-pressure refrigerant enters the evaporator, boils off, and absorbs heat, cooling the cabin air blown across it.
liquid refrigerant heads toward the cabin side and turns into gas while soaking up heat from inside. The vapor then goes back out to the engine bay, gets compressed again, turns back into liquid as it releases heat, and repeats the loop—cooling your interior as it cycles.
Controls
Temperature is regulated by how much refrigerant flow and cooling is commanded through the system.
Fan speed (airflow) is simply the blower motor RPM.
Main Components & What They Do
1) Compressor
Pressurizes the refrigerant into a hot, high-pressure gas and sends it to the condenser.
What’s happening inside
- Suction: pulls in low-pressure refrigerant vapor
- Compression: squeezes it, raising pressure and temperature
- Discharge: pushes high-pressure vapor to the condenser
Cylindrical automotive A/C compressor (e.g., BOYARD electric type), the core unit that compresses refrigerant into a high-pressure, high-temperature gas.
2) Condenser
Cools the hot, high-pressure vapor back into a liquid and dumps the heat to the outside air.
Looks like a thin radiator up front. Airflow (vehicle speed or condenser fan) is critical—poor airflow = weak cooling at low speeds.
Car A/C condenser (radiator-like plate/fin core), where hot refrigerant rejects heat and turns to liquid.
3) Expansion Valve
Drops the refrigerant’s pressure so it becomes cold and ready to absorb heat in the evaporator.
If it sticks or mis-meters flow, you’ll get poor cooling, evaporator freeze-up, or weird pressure readings.
4) Evaporator
Where the low-pressure refrigerant boils and absorbs heat from cabin air.
Air blown across the evaporator fins gets chilled and is sent into the cabin through the vents.
Evaporator core with dense fins and tubes; blower pushes air across it to deliver cool air inside.
