My car seems to have a pretty bad smell in the air conditioning. WHat is the best way to flush out these smells?
Bad AC odors are usually related to poor drainage of condensation, which allows mold to grow.
There is a small drain hose which allows the condensation to drip out, but this can get clogged up or blocked by dirt.
If this is the cause, then simply cleaning out the drain may be enough to clear things up. A quick google for your car model and air conditioner drain will probably lead you to a diagram at least, and possibly a helpful video.
If the amount of mold is significant, you might need to clean the drain pan and evaporator coil. This could involve a lot of work under the dash, which I'd rather have a root canal than do myself, so I'd take it in.
You can get products that claim to kill the mold or neutralize the smell, but these are a temporary solution at best. As long as the drainage is poor, the smell will keep coming back. Fix the drainage first, then consider options for cleaning/deodorizing if the problem isn't resolved.
It's also possible that the smell could be something else, like a fluid leak. Usually you can tell by the nature of the smell. If it smells like dirty feet, or like a stagnant pond, it's probably mold. An acrid, chemical smell could be something burning, or a fluid leak.
First, your Civic has a cabin air filter. Check it and change it because it may contain the bad smell.
That being said there are two ways to get rid of bad smells that i'm aware of, but neither is easy because you would need to a shop that has the equipment. The fist uses a machine that atomizes an antibacterial deodorizing solution while running the AC in recirculation mode to draw the mist through the system. The second uses a machine that produces ozone. Ozone is toxic to living things and kill bad smell bacterial and fungi. The treatment is usually done overnight.