What Causes the Unpleasant Odor in the Heating System?
3 Answers
Unpleasant odors in the heating system are primarily caused by accumulated dust on the filter and mold growth due to moisture. The specific reasons are explained below: Dust Accumulation on the Air Filter: After prolonged use of the air conditioning system, dust accumulates on the indoor filter and copper coils. When this dust reaches a certain level, it starts emitting an unpleasant odor. When the air conditioning is turned on, this odor is dispersed into the air through the vents. Mold Growth Due to Moisture: After cooling or heating, the indoor unit often retains moisture. If the air conditioning system lacks a dry anti-mold function and is turned off immediately, the moisture remains inside. Over time, this leads to mold growth, resulting in a musty smell.
As a regular driver, the most common cause of unpleasant odors from the heater is mold growth inside the air conditioning system. Especially after using the AC in summer, residual moisture in the evaporator and ventilation ducts creates a humid environment that fosters mold, resulting in musty-smelling air. Another issue is a dirty cabin air filter that hasn't been replaced for a long time, accumulating dust and pollutants, which reduces filtration efficiency. Sometimes, leaves or small animals can enter the ventilation system, and their decomposing remains can also cause strange odors. Having dealt with similar situations myself, I recommend checking the filter every six months and replacing it when necessary. After using the AC, run the fan in natural air mode for a while to dry out the ducts. If left untreated, these odors can trigger coughing or allergies, so it's best to have a professional perform a deep cleaning. Maintaining clean air inside the car is very important.
As a DIY enthusiast car owner, I believe that unpleasant odors from the heater are mostly caused by a clogged cabin air filter or a moldy evaporator. You can easily open the glove compartment to remove the filter—if it's covered in dirt, simply replace it with a new one. Then, use a specialized cleaner to spray into the air intake vents and run the AC at high speed to blow out any mold. Also, inspect the air intake and ducts to remove any leaves or debris. Last time I did this, the odor disappeared, saving me repair costs. Just be careful not to damage any components while working. Note that air odors can also originate from other areas of the vehicle, such as cabin leaks or foreign objects, so regular maintenance can help prevent issues. DIY-savvy friends should give this method a try.
