Found 4 Ton unit zoned system freezing up when upstairs calling for cooling and downstairs thermostat satisfied, choking unit for air. Made adjustment to bypass damper to allow more air flow when system is running. Adjusted downstairs damper to remain maximum amount open even when closed. When evaporator coil was replaced 8/2019, previous company took txv off coil and left it on top of unit. System operating properly when all dampers are open.