Performed FAU maintenance on 2 year old Lennox unit. Cleaned return grates. Flushed condensate drain with water. Inspected blower compartment, blower wheel is clean and balanced. Replaced merv 16 filter. Inspected electrical connections. Inspected flame sensor. Tested resistance of hot surface igniter. Temperature split is within limits. Installed Phenomenal Aire on return plenum and 24v transformer in blower compartment. Upon departure system is operational.