Causes of A/C System Odor

Causes of A/C System Odor

Odors from the A/C system can come from various sources. Only a portion of these odors come from the A/C unit evaporator and can be corrected by cleaning the evaporator.

Possible cause

Smell like burnt oil.

• Mostly forms in the engine compartment due to leaks on the engine or transmission.

Sulphurous smell like exhaust.

• Due to leaks in the exhaust system.

• Through exhaust fumes, which get into the passenger compartment, for example, when driving in reverse through an exhaust gas cloud.

Fishy smell like coolant.

• If fishy odor is detected also in recirculated air mode as well as in fresh air mode, check A/C system heater core for proper seal.

• From leak at cooling system of engine or of A/C system heater core.

Smell like a burned clutch.

Evaporation from floor mats, decorative seat covers, etc.

Rotten, mildewy, moldy or musty smell from the front of the vehicle.

• Due to water flowing in the case of a damaged or incorrectly assembled plenum chamber cover, cowl panel trim into the fresh air intake duct of the A/C unit. Refer to => [ Checking and Cleaning Plenum Chamber Water Drain ] Testing and Inspection.

• Due to various contaminants, such as leaves, pine needles, etc. collecting in the plenum chamber. Refer to => [ Checking and Cleaning Plenum Chamber Water Drain ] Testing and Inspection.

• Due to water that cannot drain out of the plenum chamber. Check the plenum chamber water drains. Refer to => [ Checking and Cleaning Plenum Chamber Water Drain ] Testing and Inspection.

Smell from air conditioner.

• Odors originating in the heating and A/C unit can mainly be detected in fresh air mode and recirculated air mode. If a smell occurs only in fresh air or recirculation mode, the cause is probably not the A/C unit.

• In the case of a leaking heat exchanger, the odor of the escaping coolant can be detected in fresh air mode as well as recirculation mode. However, the odor can be weaker in cooling operation than in heating operation (air does not continuously flow through the heat exchanger, but coolant continuously flows through the heat exchanger)

• Due to too much condensed water in the A/C unit, check the condensation water drain. Refer to => [ Checking the Condensation Water Drain Hose ] Checking the Condensation Water Drain Hose.

• Due to an old or dirty dust and pollen filter. Check the dust and pollen filter. Refer to => [ Dust and Pollen Filter ] Service and Repair.

• Due to deposits on the evaporator fins. Clean the evaporator with the Ultrasound A/C cleaner (VAS 6189A). Refer to => [ Cleaning A/C System Evaporator ] Service and Repair.