An air conditioner condenser unit must survive all types of weather in the yard outside your house. The condenser unit is also fairly heavy, prone to vibration and creates water as it condenses. Therefore, a solid, waterproof pad is a necessity.
The condenser unit usually sits outside the house. It contains a grid of surrounded by aluminum fins. The refrigerant that travels through the condenser is pressurized as it enters the unit, concentrating the heat that it carries from the house. As it travels through the unit, it begins to depressurize, giving up its heat, which is blown away by the fan.
Condenser units can be noisy and fans can wear if the unit does not sit level. Water from precipitation and condensation runs through the unit. Many condenser units have built-in stilts that hold the condenser and fan off the ground. The pad under the condenser unit must both support the box and keep it level through vibration and all weather conditions.
Units installed on concrete pads are solidly anchored on a waterproof base. Water drains easily through vents on the bottom of the unit. Early condensers were installed on several inches of concrete to support their large size. Cement is still a favorite pad for large-capacity units. As with most machinery that has gained in efficiency over the years, however, household units decreased in size and weight, making thick concrete bases unnecessary.
As units decreased in size, new materials were developed using green materials. These pads are inexpensive enough that homeowners can purchase new bases when new units are installed. Newer pads, formed of recycled plastic formed into pads sized to fit standard bases, are UV stable, rendering them impervious to sunlight and rain that turn most plastics brittle. Engineered, ribbed surfaces, distribute weight and cushion against vibration.