[Bones1669]

I have been renting an apartment for 7 years now. My unit is built right into the wall like you see in hotels and is also used for heating in the winter.
Yesterday I left the unit on air condition as I went out. When I returned 3 hours later, I walked past the unit and it was blowing out (to the outside) an unpleasent odor. I thought something was on fire in my house. When I came in, no smell at all was in here. The only smell was blowing outside.
I have never experienced this before. It smelled like a chemical.
I turned it off immediately and I haven't turned it back on since.

Any ideas or suggestions as to what it might be would be greatly appreciated.

Thanks in advance !