What's involved in cleaning your furnace?

Vacuum clean exterior and interior. Inspect cabinet, cabinet fasteners, and cabinet panels. Replace lost fasteners as needed to ensure proper integrity of equipment (as applicable).  Inspect the required clearance (e.g., combustion and service) around cabinet. Report instances where the cabinet does not meet requirements.
Inspect electrical disconnect box. Ensure electrical connections are clean and tight.
Ensure proper equipment grounding. Tighten, correct and repair as necessary.
Check line/low voltage.

Inspect and test contactors and relays. Look for pitting or other signs of damage. Advise replacement for contactors and relays demonstrating evidence of excessive contact arcing and pitting.
Inspect electrical connections and wire. Ensure wire size and type match the load conditions.
Tighten all loose connections and repair or replace any damaged electrical wiring.
Inspect motor capacitors. Replace those that are bulged, split, or incorrectly sized
Determine airflow across heat exchanger. Verify position of all balancing dampers. Adjust as necessary to ensure to proper airflow.
Inspect fan belt tension. Inspect belt and pulleys for wear and tear. (if applicable).
Confirm the fan blade or blower wheel has a tight connection to the blower motor shaft. Inspect fan for free rotation and minimal endplay.
Lubricate bearings as needed, only if recommended by OEM.
adjust motor speed if necessary.
Inspect condensate drain piping (and traps) for proper operation. Clean as necessary.
Inspect burner and flue for signs of water, corrosion, and blockage. Identify cause and clean, repair, or replace as necessary.
Test inducer fan motor and blower assembly.
Inspect heat exchanger for signs of corrosion, fouling, structural problems (e.g., cracks,  perforations, and bulges), and erratic flame operation during blower operation. Identify cause notify homeowner.
Visually inspect burners for signs of contamination. Clean, or repair as necessary.
Inspect hot surface igniter for cracks, check cold with ohmmeter and proper supply voltage. Replace if outside OEM’s specifications.
Measure and adjust manifold pressure as necessary. Adjust the gas valve to provide proper manifold pressure.
Inspect ceramic insulator, flame probe, and associated wiring for any cracks or abnormalities. Clean according to OEM recommended procedures.
Test main burner ignition sequence and flame safety; verify proper operation.
Test burners. Fire unit and adjust air shutters (if used) for OEM specification compliance.
Inspect the spark igniter and associated wiring. Verify that spark gap complies with OEM
Ensure combustion air volume or provision is correct.
Measure TD across the heat exchanger. If TD is outside OEM’s specifications, identify cause and then clean, repair, or replace as necessary.
Inspect vent exhaust system (e.g., chimney, chimney liner, flue, inlet and exhaust vent) for signs of improper condensation, water corrosion, cracks, fractures, and blockages.
Clean, remove blockages as necessary. Inspect all vent connectors for rust discoloration, or signs of condensate.
Inspect inlet and exhaust vent pipe for proper support, slope, and termination. Repair or replace as necessary.
Inspect for combustible materials placed too close to vent or pipe.

Air Distribution System

Inspect for particulate accumulation on filters. Clean or replace filters if accumulation results in PD
higher than design or if airflow is outside of established operating limits.
Inspect air filter housing integrity and air seal. Correct as needed.
Inspect trunk/branch sizing.
Inspect all accessible ductwork for areas of moisture accumulation or biological growth.
Inspect the integrity of all accessible ductwork including: duct strapping, hangers, sections, joints, and seams. Note improper alterations, straps, air leaks.

Controls and Safeties

Test modes of operation and control sequences. Test system control devices to ensure they are maintaining their expected range.
Test unit safety switches. Repair wiring or replace safety switch as needed.
Verify that all selectable pins, jumpers, and/or dip switch positions on control board are correctly
positioned for the application.

And of course address any concerns you may have and make recommendations to improve comfort and efficiency!