Performed furnace maintenance on 9 year old carrier 98 percent system. Met with Marcus, homeowners not present. Cycled both zones for heat. Checked indoor unit electrical and system components. Verified proper heating sequence of operations. Temperature rise across heat exchanger is within range. Ran system through 20 point inspection checklist. Cleaned off filter return register. Furnace exterior is covered in foam insulation that can not be cleaned off. Could not go over findings and recommendations, will be emailing everything to homeowner. Cycled system, system is operational upon departure.