Upon arrival tenant advised me that heat was only blowing cold air and was coming on and off. After inspection of system found that system had a failed heat exchanger. Unit is 33 years old (1993) both ac and heat. Duct system is in very bad shape, there are a lot of duct runs with holes inside them and insulation is showing on the duct runs. Inside system blower wheel and motor are very impacted causing air flow to be very minimal inside system. The high limit is activating due to furnace temperature exceeding 155 degree that rated on data plate. Temperature is reaching 170+ and activating high limit switch. Plenums are very dirty and need to be updated. Tenant stated ac unit struggles a lot durning summer, the evaporator coil is very rusted and potentially leaking refrigerant. Spoke with landlord in regards to issue with equipment. Recommended rep placing full system both heat and ac and also replacing the supply plenum, return plenum and duct runs. Customer approved to speak with ins