Performed FAU tuneup on 3 year old Lennox unit. Cleaned return grates. Inspected filter. Flushed condensate drain line. Inspected blower compartment, blower wheel is clean and balanced. Inspected electrical connections. Tested all safety switches. Cleaned in place blower compartment. Tested external static pressure and found it to be high, I noticed a couple of supply vents closed and this may be causing the pressure to be a bit high. Inspected flame sensor. Tested resistance of hot surface igniter. Temperature rise is within limits. Upon departure system is operational.