The glass can either be etched with hydrofluoric (HF) acid or sandblasted.

Is throwing acid in someone's face evil?

., condensation on AC coils or water in your lungs) to form sulfuric acid (H2SO4) and hydrogen gas (H2).

Urine is sterile and highly acidic, and once the ammonia smell and the water evaporates the remainder is mostly salts.

If you are wondering what pets do to the central AC units, here is something a little more than just speculation.I have a triplex, where each unit has the same exact central AC handlers and condensers and same age.December 2014, I had an air conditioning company cleaned all three evaporator coils - pulled the coils out and acid wash them.Here is a picture of what the coil looked like immediately after the cleaning.I personally change the filter in all three units once a month.Now, only eight months later, units 1 & 2's coils look about the same with just a little more dust.Unit 3's coil look like this.Same size apartment, same central AC units, same age, all cleaned at the same time, had filter changed by me every month at the same time.The only difference is unit 3 has two dogs, one 40 pounds and one 50 pounds.I am not against pets, but thought I would share this.

Apparently condensate from a Hi Efficiency Fce can have a pH ranging 3.5-6.5, effectively 10x more acidic than tap water.  

We have tried to use that before, but at least one time the repairman didn't get what we were doing and poured strong acid into the drain before we could get the camera down it.

When a compressor fails it burns the oil out and can turn acidic when you install a new compressor.

I'm not a fan of flushing agents, but 410a reverts to an acid at the slightest sign of moisture or contamination and makes a substance that clogs all of your components of the system and it's a royal pita to get that contamination out.

Be careful using Draino type product cause the are acidic, if you have metal pipes don’t use it at all.