Upon arrival to scheduled system maintenance I was shown to a A/H unit located veritcally in a closet space. Pulled panel doors off the unit to inspect all electrical connections, collect electrical readings and check the evap coil for cleanliness. Evaporator coil is clean with pictures uploaded to ST. All electrical components connections are secure and readings are within range of specifications. I am recommending some type of UV purification for the air handling unit inside to negate biological/microbial growth build up to keep the system clean. No attic access to view duct work at this time. Collected temperature differentials in cooling mode, and verified functions in the heating mode. In the cooling mode had a 20° delta T. And then the heating mode had 82° at the supply Plenum. Went to the side of the building to the C/U to verify system refrigerant charge, inspect all electrical components connections, and collect electrical readings. Outdoor unit is not surge protect