When the evaporator coil is housed in a separate casing that contains a blower for circulating the cool air, the coil is commonly referred to as a blower coil. Most often, the blower coil is located in the attic. However, it can be located in a closet or in the basement. The blower coil should be vibration-mounted to prevent the noise of the blower unit from being transmitted into the living area. Vibration mounting can be achieved by placing the unit on rubber, cork, or styrofoam pads. (See FIG. 17-5.) The vibrations might also be isolated in the attic by suspending the unit from the roof rafters.
The base of the blower coil is basically a condensate collection pan. The accumulated condensate is removed by means of a drain line that will extend through the exterior wall, terminating on the outside, or extend through the lower portion of the roof, terminating in the gutter. Sometimes the condensate drain line terminates in the plumbing vent stack located in the attic. (See FIG. 17-6.) In many communities, this type of termination is not permitted because it is not in compliance with the plumbing code. If the drain terminates in the vent stack, record that on your worksheet. The legality of this type of connection should then be verified with the local building department.
The purpose of the vent stack is to channel sewer gases in the plumbing system to the outside. If the condensate drain line is connected to the vent stack and there is no trap on the drain line, the sewer gases may back up into the condensate drain line, enter the blower coil, and be circulated throughout the house. The condensate drain line should have a U-shaped trap near its connection to the blower-coil housing. On many installations, this trap is omitted. Look for it. If it is missing, one should be installed.
When the blower coil is located in the attic, certain steps must be taken to prevent cosmetic damage to the ceiling below in the event of a blockage in the main condensate drain line. Some blower-coil housings have a fitting for an auxiliary drain line that is located just above the main condensate drain fitting. If the main drain becomes clogged, the level of the condensate will rise and be drawn off by the auxiliary drain.
For those blower coils that do not have a fitting in the housing for an auxiliary drain line, there should be an auxiliary drain pan below the unit. The auxiliary pan will collect any condensate that overflows from the main pan when there is a blockage in the main drain line. Look for an auxiliary drain pan. In some parts of the country auxiliary drain pans are installed when the blower coil is located over any furred space, even when the blower housing has an auxiliary drain fitting. Record the absence of one on your worksheet. Unfortunately, many air-conditioning contractors do not install the auxiliary drain or drain pan. Because rising costs make it difficult to remain competitive, they cut costs wherever they can.
The auxiliary drain pan must have a separate drain line that discharges to the outside. It should not be connected to the main drain line. (See FIG. 17-7.) If it is, it reflects poor-quality workmanship; if the main drain line becomes clogged near the discharge end, the auxiliary drain line will also not function.
If the evaporator coil is accessible, it should be inspected for frost buildup. From an efficiency point of view, the attic is the least desirable area for locating the blower coil because of the high temperatures, easily reaching 140° F to 150° F that normally occur during the summer. Even though the blower coil is insulated, there will be a heat gain because of this high temperature. The overall attic temperature, however, can be lowered by increasing the number or size of the attic vent openings. A ridge vent is quite effective, as is a thermostatically controlled power ventilator.