Performed system diagnostic on carrier evaporator coil. Upon my diagnostic client stated that entire upstairs system smells like a dead rat is inside the duct work creating a odor that is overwhelming preventing them from sleeping upstairs. I first started by checking the filter and found that it was completely plugged up and dirty, Also every single supply vent was sealed up preventing airflow from coming out. I made my way to the evaporator coil in the attic and open the case. Found no evidence of a dead rat but the drain lines are completely clogged up and show signs of dirt buildup and debris within the coil that can cause a smell to linger throughout the house once moisture builds up in cooling mode. Recommended To prevent any smell or mold/bacteria buildup inside the evaporator coil that a phenomenal air is installed into the supply Plenum of the coil. Provided information on the process of how this works and recommended that a maintenance plan is also done to keep the system at