I will explain what negative air duct cleaning is in another article but for now this is how to clean an return line step by step.
1. The first step is to take the return vent cover off of the ceiling, floor, or wall, depending on the configuration of the home and system. As soon as the cover is off ensure that it is washed off outside with a hose and left to dry or HEPA vacuumed for re-installation.
2. After removing the vent cover the 8 ", 10" or 12 "suction hose to the plenum of the HVAC unit is ready to be attached. This hose should already be attached to the negative air duct cleaning machine. attached with a few different methods. If the plenum is constructed out of aluminum like most, take the circular whole cutter and create the appropriate whole to fit the suction hose flange.
3. Next take the locking collar and attach it to the whole which has just been opened. When the collar is attached the suction hose is ready to be attached to the collar. Make sure there is a good connection to the plenum to ensure there will be no air leaks.
4. Now that the line is attached the system needs to be isolated. This can be done in a couple of fashions. Companies can block each supply line but when there are over ten or so this can be time consuming. To accomplish this task the air filter which is between the return plenum and the blower can be placed into a garbage bag and then re-inserted. This will block the air from pulling from the supply lines. This is not a perfect seal but you are only dealing with one return line so adequate air flow is easy to achieve. If the system has room to allow for an inflatable isolation bag, use it for a maximum system seal.
5. The return line is now isolated and the negative air duct cleaning equipment is set up and ready to perform. Turn the machine on and check for air leaks by the connection. Also go to where the vent has been removed and ensure there is proper suction airflow going into the return vent.
6. The line is ready to be cleaned at this point. Companies can now either use a rotary brush or an air whip line to clean out the return line. These tools are inserted into the opening where the vent cover gets attached. Ensure the equipment is ran all the way back to the plenum for maximum contact and cleaning. This procedure will clean out the return line of an air conditioning and heating system.