I have an old wall unit in my apartment (renter). It’s at least 12 years old as that’s when I moved in. What happens is that after I turn it on, ice, or some other whitish substance starts to coat the inside of it. It doesn’t take long for the icy substance to appear, just a few minutes. If I let it go for about an hour, I’ve pretty much got a polar ice cap in my air conditioner.
Is there something leaking? Something not good for me? Is this is a sign that the unit is about to die? Is it hurting its energy efficiency, which is pretty bad to begin with.