Customer has 2 y/o 3-zone Goodman system that operates for whole house. Furnace located in garage closet. According to customer, system will overheat at times, however, has not since 20x25x1 filter was replaced. Noticed that return ductwork is insufficient for system. Furnace is 100K BTU. Evaporator coil is 5-ton with 4-ton AC. Return is only 1400 CFM. System has 10” bypass damper located on backside of system with limited access. Dampers are located in a limited access attic. Adjusted dampers to not fully close to assist bypass damper with excess heat. Recommend ductwork modification for proper airflow. Informed customer of all findings. System is currently working.