Cars always smell when heated in winter. What is the reason and how to deal with it?

The main reasons for the smell of hot air are:

The air filter of air conditioner is dirty. It may be caused by not replacing the air filter of the air conditioner for a long time. It is recommended to disassemble the air filter of the air conditioner for inspection. If it is too dirty, it is recommended to replace it.

Dirty air filter of air conditioner leads to odor in the car. It is suggested to clean the air conditioning pipeline while replacing the air filter of air conditioner, which can effectively remove odor and keep the pipeline clean.