Chemical damage to your outdoor unit whether a heat pump or condensing unit can be seen in this photo. Notice the damage to the coil causing a refrigerant leak. This damage was caused by the family dog repeatedly peeing on the unit. Dog urine kills A/C units. This kind of damage is not covered by the manufacturers warranty. This unit was only 4 1/2 years old, leaving the homeowner with a very expensive solution.
Damage can also be done by liquid lawn fertilizer. Technically also by the grandular kind. It is best to turn off the A/C when spraying or applying lawn chemicals so the fan will not suck in the chemicals. And train the dog not urinate on your A/C unit.