i have a 1994 eldorado that whenever it wants to the dash locks up, when this happens the heater will go to ac when cold out or heat when ht out.cannot control anything and nothing works except speedo and tach.help please

im having a smalier probelm but not just heater control the fuel ranger the mile per gal the outside temp and the engine temp where there sould be # thay go blank to - - - than the heater blows hot when hot out and cold when cold out some times it come back in and works but then it drop out again please help