What Are AC Evaporators?

AC evaporators are crucial parts of your car's air conditioning system, usually found inside the passenger compartment under the dashboard. In vehicles with rear air conditioning, there might be two evaporators: one behind the dashboard and another at the rear. The main job of the evaporator is to remove heat and moisture from your vehicle’s interior. There are three main styles of evaporators: tube and fin, serpentine, and plate and fin.

Tube & Fin Evaporator

Serpentine Evaporator

Plate and Fin AC Evaporator

How It Works: Low-pressure refrigerant flows into the evaporator. The blower motor pushes hot air from inside the vehicle through the evaporator fins. As the refrigerant absorbs heat from the air, it changes from a liquid to a gas. This heated refrigerant then travels through a hose to the compressor. The compressor pumps it into the condenser, where it releases the absorbed heat, turns back into a liquid, and the cycle repeats.

The evaporator also dehumidifies the air inside your vehicle, enhancing passenger comfort. Moisture collects on the evaporator fins during the heat exchange process and drains out through a tube beneath the vehicle. You might notice a puddle of water under your car when the AC is running—that’s normal.

AC System Designs: There are two types of AC system designs: orifice tube systems and expansion valve systems. Both rely on the evaporator to remove heat from inside the vehicle. If the system is low on refrigerant, it will "boil off" faster than it should, failing to remove all the heat from the cabin and potentially leading to compressor damage due to insufficient oil return.

Maintenance Tips: Excess moisture can harm the evaporator. It frequently gets wet and dries out, trapping dirt and debris that can lead to mold. This buildup can reduce the evaporator’s efficiency by blocking airflow and causing corrosion. This issue is common in areas with high humidity, where evaporators may need frequent replacement.

During the heat exchange process, the evaporator removes heat and moisture from the air inside the vehicle, causing moisture to condense on the evaporator and its fins. On humid days, this can lead to a puddle of water forming under the car, usually on the passenger’s side. This moisture flows from the evaporator to the outside via a drain tube.

Over time, dust and other particles can accumulate on the evaporator fins. This problem can be exacerbated if pets are transported in the vehicle or if the driver or passengers smoke. The blower motor pushes air across the evaporator fins, and particles can get lodged in the fins, mixing with moisture and potentially causing bacteria, mold, and fungi to form. These can create a smell and block the fins, reducing the evaporator's efficiency.