Arrived on site to perform furnace diagnostic on 17-year-old package unit. Initially technician arrived prior and diagnosed the pressure switch was not closing and reset System, soon after unit Began Heating. Client now states that unit is doing same exact thing and only lasted six hours after technician left. Began diagnostic and found same error code present and reset unit and unit began heating. After running for about 5 to 10 minutes system was already out putting a 80 degree temperature rise. Unit is now overheating and past it’s max temperature rise rating of 75 degrees. Inspected size of unit and found that it was rated for 135,000 BTUs when the house is only 1900 Square feet. Package unit is significantly oversized And was retrofitted from a horizontal furnace to a package unit design to the side of the house. Due to installation from 17 years ago and oversizing unit, there is not much we can do besides downsizing to a 4 ton. Unfortunately unit will continue to overheat and h