Check and adjust thermostat.
Check to make sure that the indoor & out doorunits come on, which includes the furnace.
Replace the air filter or clean if reusable type.
Check bearings & lubricate blower motor if needed.
Check blower belt, wear, tension & adjust as needed.
Check electrical connections for tightness.
Check evaporator coil to determine if it needs cleaning.
Check voltage to unit.
Check blower motor amp draw.
Check electric heaters with amp probe and voltage during heating inspection.
Check condenser motor bearings & lubricate if needed.
Check condenser motor amp draw.
Check refrigerant (freon) level.
Check compressor amp draw.
Check crankcase heater if compressor has one installed.
Check defrost controls.
Check reversing valve operation.
Check coil temperature.
Check the flue for rust & corrosion and advise of discrepancies.
Check flue for satisfactory operation.
Check, clean, and adjust pilot if needed.
Check electronic spark ignition control for proper operation.
Check and adjust burners for fuel efficiency.
Check heat exchanger for cracks, soot, & rust.
Check heat exchanger for cracks when the furnace is hot.
Check blower motor & induce draft motor amps.
Check manifold pressure.
Check fan controls
Test safety shut off response.
Check condensate drain and pan then advise of any discrepancies.
Perform visual inspection of ductwork and make notes regarding discrepancies.
Check the shape that the total system is in and note any discrepancies.