air-conditioner was already a synonym of air-conditioning. That's noticeable when you try to go to the air-conditioner tag and it's all the air-conditioning questions. I've gone ahead and merged that one.
I've also edited the one question with air-fil to use the correct air-filter. I'm guessing that was from using the wrong key to auto-complete, and the system would have eventually deleted it.
If there are other specific entries that need to be defined as a synonym, please raise those as individual suggestions. What I'm looking for is all posts with one tag fitting within a better tag, and no additional value from the original tag.
You can see all the tag synonyms at: https://diy.stackexchange.com/tags/synonyms