Performed diagnostic on main floor 25 yr old Lennox unit, Upon arrival customer stated unit wasn’t heating, checked tstst, cycled to heat mode, upon going in attic found unit heavily rusted in secondary drain pan as well as inside furnace cabinets, burners are heavily rusted as well as evap coil and heat exchanger, control board giving pressure switch code, upon inspection found pressure switch and high limit switch jump out, explained to customer that is a safety hazard, checked high limit checked ok, but pressure switch is failed, inducer motor heavily rusted and pulling high amps, recommend replacing inducer motor as well, blower wheel heavily rusted, recommend replacing blower wheel housing and blower motor, explained with all repairs furnace can still fail due to age and conditions, also explained r22 is obsolete as of 1/1/2020, unit is not safe to run at time, turned off a tstst and recommended customer not trying to run unit, highly recommend system upgrade and having install su