Smell of plastic (synthetic)
Usually felt the first time a newly installed appliance is turned on. This disadvantage is often found in cheap devices. The smell disappears after a few days of use and is not considered an indicator of a malfunction of the appliance. However, you should make sure that the plastic does not melt in an air conditioner (usually in heating mode). This can be the case when using low-quality plastics in the manufacture of air conditioners.
Smell of burnt insulation
If you smell burning when you turn it on, then unplug a device. It is possible that the wiring has burned out and it precedes an imminent breakdown of a device, which can also lead to a fire. A technician is called to resolve this problem.
I don't know any more reasons.
Finally, if you suddenly stay/cannot use your air conditioner, there are other cooling methods.
