How to Clean a Car's AC Evaporator

by Craig Woodman
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Adrián González de la Peña/Demand Media

According to "Motor Trend" magazine, the inside of your car can contain up to 10-times more pollutants and contaminants than the air in an equal volume of space outside of the car. Manufacturers have worked to overcome this in recent years with improvements in cabin air filters and air ducting. A common source of problems is the air conditioning system. The AC evaporator becomes wet as humid air is passed over its cool surface. This wet enviroment is a good place for mold and mildew to grow and for dust and pollen to collect, finding their way back into the air system. Bacteria grow exceptionally well in this area, which becomes warm but still damp when you shut the car off. This contamination should be cleaned regularly.

Step 1

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Inspect your vehicle's air conditioning system under the hood. You are looking for the evaporator/heater box assembly. This is on the firewall that separates the engine compartment from the passenger area. It will be a plastic encased box that protrudes outward from the firewall. The heater-blower motor will be attached to it. You are looking for the easiest way to access the air conditioning evaporator core.

Step 2

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Access the evaporator core. Many vehicles have a resistor block that mounts on the top or side of the heater box. You may be able to remove this for easy access. You may also want to consider removing the blower fan and see if you can access the evaporator core. If neither one of these methods will work, you can drill a 3/8-inch hole between the evaporator case and blower fan. This will be sealed later. You need a direct pathway to cover the evaporator core in cleaner.

Step 3

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Spray the cleaner through the access point towards the evaporator core. If you can see the core to cover it completely, that is the best way. Many of these cleaners are foam based, which manufacturers design to cling to all of the surfaces inside of the heater box, cleaning and disinfecting them. Fill the area with foam and let it set for at least one-half hour. The foam will turn liquid and pass through the drain openings when it has completed its cleaning job.

Step 4

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Lightly rinse the area with water. You may use a light spray from a garden hose. Have a helper watch the inside vents while you do this because you can spray water inside of the car. If you are not comfortable with the hose, use a spray bottle containing clear water to provide an extra rinse.

Step 5

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Seal the heater box. Install the resistor block or blower fan if you removed them. If you drilled a hole, use RTV silicone from a tube to seal the opening. When you want to clean the evaporator again, just pick the dried silicone out with a pick or screwdriver to access the core. Run your vehicle for half an hour with the heater set to hot and the blower on its highest setting to dry the area completely.

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