only blows cold air

A cable that runs from the console heater temp control to a valve in the engines coolant system may be broke or have become disconnected from it's linkage at either end. That valve controls the amount of hot coolant going into into the heater core. On older vehicles, it was a piece of cake to fix the problem. On todays vehicles it almost takes an engineer to figure out how to get to the cable either behind the console or even in the engine area. Good Luck.