The reason why the water is dripping from the ceiling or pipe is because the primary drain line that is attached to the evaporator coil drain pan is clogged. Clogging is a sign the primary drain line needs to be cleared either at the unit or the p-trap under the bathroom sink.
How does a clog happen?
Clogs happen and it is fairly common. Debris from the filters not being replaced on a regular schedule can cause drain issues. Attic particles such as insulation, dust, rodent waste, bugs, and plastic to name a few that clog the secondary drain line and usage of the HVAC system without routine maintenance.
How often should the HVAC maintenance be performed?
Your air conditioning and heating system needs to be maintained twice annually. One spring / summer tune up for cooling and one fall / winter tune up for heating.
No matter how many systems you have on your home, each central air system will need to have routine maintenance. A routine check up bi-annually will thoroughly evaluate the electrical, refrigerant and the drains.