A method for cleaning, sanitizing, and disinfecting commercial and residential HVAC system includes applying low pressure cleaning foam to heat-exchange coils of the HVAC system, the cleaning foam including one or more agents that break down organic and/or inorganic fouling dirt or debris, the foam removing and carrying away dirt or debris from the coils. Moving air, such as from the air handler of the HVAC system, pushes or draws the cleaning foam from the first side of the coils toward a second side, the cleaning foam and removed dirt or debris exiting the second side of the coils. The moving air and cleaning foam move co-currently in the same direction through spaces in the coils.