Checked all operations in heating mode and inspected the furnace filter. Checked static pressure and found that it wasnt passing so the customer and I went around the home to make sure all vents were open. The unit didn’t have no dampers on it and no clean filter. I didn’t have the right size filter on the truck. So I did the retest and the static pressure was still not passin so with customers approval we will have a field supervisor come out to evaluate. Checked all electrical components and preformed an combustion analysis. I checked the heat exchanger it had no rust spots and no cracks in it. The blower wheel had buildup and dirt on it but the customer didn’t want to do anything at this time. All electrical components were operating properly and the furnace fuel was burning properly as well.