- Water is condensed by the cold refrigerant in the evaporator coil.
Coil and Pan
- The condensed water drains down the coil and collects in the main condensate pan. The evaporator coil rests on the bottom of the main drain pan.
- Typically, the bottoms of the pans are flat and horizontal with an opening on the side for attachment of the drain line.
- Installing the coil and pan to be level causes mold growth in the pan because of the holdup of water in the pan. A dry pan with no visible mold growth is achieved by installing the coil with a good pitch toward the outlet end of the pan.
Main Drain Line
- PVC, schedule-40 pipe, either 3/4" or 1" diameter, is normally used for the drain lines.
- Code requires the pitch to be one quarter inch (1/4") per foot of length to eliminate water holdup in the pipe. Use 1/2" pitch or more.
- The main drain line is allowed to terminate along side of the home in the yard or in a flower bed. Into an undergound drainage system is better.
- Termination may also be indoors into the trap of a lavatory, tub, shower, or commode.
- Insulate the main drain line with 1/2" insulation per national code.
- A water hose is best to clean the drain line. Air or nitrogen does not break loose and flush out the mold, a white, jelly-like growth.
Trap the Main Drain Line
- Evaporator coils placed before the blower have a negative pressure and will suck air in from the main drain line. The main drain line must have a trap filled with water to prevent bad air from entering the home. See
- If you have a gas furnace, the evaporator coil is after the furnace which contains the blower. The evaporator coil is under positive pressure. No air will be sucked in. Cold air will be blown out through the main drain line. Often the small lines are more than 30 feet long which prevents much air from escaping. A trap may or may not be used.
- Traps are the source of most pluggage in main drain lines. They are filled with water all the year round and provide a fertile medium in which the "jelly" can grow.
- Termination into an indoor trap associated with a lavatory, etc. definitely eliminates the need for a trap except for noise. The air blowing through the main drain line causes gurgling and bubbling noises if the traps have been improperly installed.
- Because traps so readily plug, put them at the lowest point of the main drain line so that the build up of the water level may flush out the plug before the main drain pan overflows.
- Install a "tee" in the main drain line to facilitate flushing and to allow adding bleach to the trap.
Emergency (secondary) Drain Pan
- To prevent damage to a ceiling from the overflow of a main drain pan, code requires the use of an emergency drain pan under the main drain pan.
- Drains from emergency drain pans are required to drain from a high point in a visible area so that they will be noticed. A call for service of the unit will then prevent ceiling damage.
- Float switches in the emergency drain pan shut off the entire system to attract the attention of the occupants in cases where both drain lines have plugged. Request one.