Evaporator Core

The evaporator is the heat exchanger located inside the vehicle's HVAC (heating, ventilation, and air conditioning) housing behind the dashboard, through which cold, low-pressure refrigerant flows while cabin air is blown across its fins. As the liquid-vapour refrigerant mixture evaporates in the evaporator coils, it absorbs heat from the passing air — cooling and dehumidifying the air before it enters the cabin. The evaporator typically operates at −5 to +5°C surface temperature, causing moisture from the humid cabin air to condense on its fins. This condensate is collected in a drain tray and expelled from the vehicle through a drain tube to the outside. The evaporator's dual function of cooling and dehumidification makes it responsible for both the comfort cooling and the defogging capability of the AC system — running AC in defrost mode uses the cold evaporator to remove moisture from the warm, humid interior air before it reaches the windscreen.

The evaporator is where the AC cycle's useful work occurs — all the heat absorbed by the refrigerant circuit is drawn from the air crossing the evaporator surface. The temperature difference between the refrigerant (below 0°C) and the cabin air (25–35°C in warm weather) drives a high rate of heat transfer across the evaporator's aluminium fin-and-tube matrix. Simultaneously, the sub-zero surface temperature causes water vapour in the air to condense, reducing the humidity of the cabin air. This dehumidification is as important as the temperature reduction for thermal comfort and for windscreen clarity — on a cold rainy day, running the AC provides dehumidified air that prevents condensation on the windscreen interior, regardless of whether cooling is wanted.

Musty or mouldy smell from HVAC vents when AC is first switched on: Bacterial and fungal growth on the damp, dark evaporator surface between AC uses. The moist evaporator is an ideal growing environment when the fan is off. Running the fan without AC for the final 3–5 minutes before parking allows the evaporator to dry, preventing growth. Annual evaporator disinfectant spray treatment eliminates existing bacterial colonies.

Water dripping from the HVAC housing onto the passenger floor: Evaporator condensate drain tube blocked by leaves, debris, or algae growth. Condensate overflows the drain tray and leaks into the cabin. Clearing the drain tube (typically accessible from under the vehicle) resolves the leak without any refrigerant circuit work.

AC cooling reduced despite other components functioning: Evaporator fins partially clogged by dust and debris drawn through the cabin air filter — replace the cabin air filter and clean the evaporator with evaporator cleaner spray if accessible.

Level 1 — Owner check: Run the cabin blower fan only (AC off) for 3–5 minutes before switching off the engine on any journey where AC has been used — this dries the evaporator surface and prevents bacterial growth. Check that the condensate drain tube beneath the vehicle is clear — water dripping from under the vehicle after AC use is normal; water dripping inside the cabin is not.

Level 2 — Detection: Replace the cabin air filter every 15,000–20,000 km — a blocked cabin filter reduces evaporator airflow, reducing cooling efficiency and causing the evaporator to ice. Use antibacterial evaporator treatment spray annually (sprayed into the cabin air intake with the fan running and AC on) to address bacterial growth without disassembly.

Level 3 — Professional service: Evaporator replacement is the most labour-intensive AC repair — requiring complete dashboard removal on most vehicles. A refrigerant leak at the evaporator (detected by oily residue inside the HVAC housing or UV dye visible in the condensate) is a significant repair. Prevent leaks by maintaining correct refrigerant charge — a system run with low charge runs at higher pressures that accelerate seal degradation.