Came out today for a ac issue. Upon inspection I found that the thermostat is jumping temperature constantly. The homeowner stated that she has lived here for 20 year and has never changed the thermostat. I replaced the old Honeywell thermostat with a new Honeywell t4 thermostat serial #2150jjc09905. Once the thermostat was connected I tested the system by calling for heat the calling for air. Both started without any issues. The ac temperature split is at a 20.