Furnace repair and completed cooling preventative maintenance check. Find gas furnace was off on safety. Reset and system operate. Find gas pressure low, worn ignition, weak flame sensor, worn inducer assembly. Find door switch damage. Find gas line not up to code and flue pipe not up to code. No water protection. Find ac unit operating but oil have acid buildup. Find fan motor not balance, worn contractor. System line set not size properly for system. Due to system age and multiple conditions can cause system to fail. Suggest to upgrade system.