First let me begin by explaining how your central air conditioning system is installed. Most people don't realize systems today are actually split systems. The first half of the system is the compressor, which is located outside, usually at the rear or side of the home. The second half are the cooling coils and blower, which is located at the furnace. Yes, the furnace and A/C system share the same blower, which circulates the air through your home. The furnace/blower is typically located at an interior closet, garage, attic and or basement areas. If your home doesn't have a furnace you may have an air conditioner which can work in reverse, this type of system is called a heat pump. A heat pump looks just like a regular split A/C system, but instead of having a furnace; you only have the cooling coils and blower.
The refrigerate cycles through the system from the compressor to the cooling coils and back again. Condensate or water builds up in the housing, which houses the cooling coils. This water must drain to the exterior or a drain (usually underneath the bathroom sink). The drain lines for the condensate are typically white PVC pipes. There should always be a primary and an alternate condensate drain line, just in case the primary clogs. If your furnace and cooling coils are located in the attic and the drain line clogs, you may experience leaking and water damage at the ceiling or walls. Even if the cooling coils are located above furnace in the garage, leaking can damage the furnace. This is why it is a good idea for you learn which drain line is your alternate. For example, if you see water dripping from the alternate, then you know the primary is clogged. Always call for service before the alternate clogs and damage occurs. You can ask you're A/C contractor to identify the alternate. Often times the primary and alternate are connected or the alternate is not even installed. If this is the case, correction is recommended.
Here are some basic things to consider regarding the compressor, which is located outside. Make sure this unit is level and elevated 3 inches above the ground on a platform. This will help prevent the unit from rusting or corrosion from the bottom. Also make sure it is at least 6 to 12 inches from any walls or obstructions, to allow for adequate air flow. If the air flow around the compressor is inadequate, it can affect the efficiency of the unit. The last thing anyone wants is a higher electrical bill, due to personal items or vegetation growing on the compressor.
As always change your air filters once every 3 months and service the system once annually.
Article courtesy of Duane Morrison, Morrison Home Inspections