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DIAGNOSE – ODOR COMING FROM AIR CONDITIONING VENTS
By Carl O’Reilly

SYMPTOM SUMMARY
A mild to severe odor that emanates from the air conditioning vents shortly after starting the air conditoning. The odor may diminish after the air conditioner has been running for several minutes but reoccurs at next operation.

USUAL CAUSE
Odor from the air conditioning is usually caused by mildew growth on the air conditioning evaporator core. During normal A/C operation, water condenses on the evaporator core. This water is drained off through a tube located at the bottom of the evaporator housing in the passenger compartment. Small amounts of water will remain on the evaporator core after the air conditioning is turned off. On a hot day, this moisture inside the evaporator case can cause mildew growth on the evaporator core. This mildew growth can cause a foul odor through the air conditioning vents during the first few minutes of air conditioning operation. It can smell like dirty feet or stinky socks.

CORRECTIVE ACTION
There are several industrial chemicals that can be used to kill the mildew growth, but it will usually require perodic treatments at the peak of the air conditioning season. Household mildew sprays can also help by spraying a fine mist into the vent inlets, usually located on the exterior of the vehicle near the windshield. This procedure should be done while the fan is on high, all windows in the vehicle open and the recirculation switch on the dash set to outside air. The purpose is to draw the cleaner past the evaporator core killing any mildew present on the surface. Use the cleaner sparingly and never spray it directly into the vents located in the passenger compartment.

PRECAUTIONS, TIPS, and NOTES
Completely ventilate the vehicle of any cleaner fumes prior to driving with the windows up. Use caution with the cleaner not to damage the paint or interior of the vehicle.


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