It is clear that you were in attendance to WITNESS ONLY ONE (Step 7) OF THE 10 STEPS required to effect a thorough furnace/AC coil cleaning which would require your undivided attendance & attention for about 15 - 20 minutes.
Step 1: While 8" vacuum is hooked up to supply run, inducer & blower motors are blown out with high pressured air, using caution not to damage igniter switch. Burners follow using the same procedure with reduced air pressure.
Step 2: AC coil is accessed above or below, gently blown out with reduced air pressure, scraped clean with wire brush, sprayed with AC condenser coil cleaner/disinfectant, then scraped and blown out again.
Step 3: Portal is most commonly resealed with a new galvanized steel plate, new screws and aluminum foil tape.
Step 4: 8" vacuum hose is brought down to combustion chamber and blower compartment. No damage is effected using reduced air pressure to gently blow clean all wires and connections and computer mother board.
Step 5: Upper & lower chamber floors are blown clean with high pressure air.
Step 6: HVAC approved cleaning solution is sprayed onto floors, walls, blower housing, on & inside burners, then wiped clean with shop towel.
Step 7: Cleaner is applied cautiously to all wired connections and burners. Using a brush, all components are gently scrubbed, then wiped clean with a shop towel.
THIS IS THE ONLY STEP YOU WITNESSED.
Step 8: Connections & safety switch are inspected for security and positioning.
Step 9: Front and back surfaces of upper & lower compartment doors are sprayed with cleaner, wiped clean, then refitted.
Stage 10: Furnace or AC is turned on to check that HVAC unit is functioning well.
Reply created 7 Jun 2017