Urine damages condenser coils
Urine is acidic and will quickly damage your air conditioner, especially if the unit is running when your pet piddles on it. The fan will suck the urine through the coils and distribute it inside the cabinet, causing unseen damage.
This kind of damage significantly affects system performance and lifespan. Removing the animal from the area will not stop the corrosion from progressing. Unless the entire unit is professionally cleaned (hopefully in time) the final result may be replacement of the unit - which usually means replacement of the entire central air conditioning system. Warranty replacement would be unlikely.
Ensuring your pet barrier is high enough to keep Fido off the machine, it should be placed not less than 1 metre from the unit, and constructed in a fashion which will allow unimpeded airflow. Don't forget to include a gate for access to clean or service your air conditioner, and to cover it before winter arrives.
A great idea:
New air conditioners are often installed on a wall rack, at a height well above the dog pee range - which also minimizes accumulation of leaves, grass and other debris inside the unit, as well a guarding against physical contact with lawnmowers, garden tools and hockey pucks.