Heater is blowing full blast cold air

We just got this car and had to put and alt. And battery in it. Now on the instrument panel the fuel reads on the instruments for the fuel read out and the heater controls it reads "c" the heater is blowing full blast cold air and no matter which button you push it will not change or even cut off. What could be the problem. Like I said we just got the care ait needed an alternator and battery now like I said above the fuel gauge instrument will not change if we put fuel in it just reads"c" and the heaqter will not cut off just blowing cold air on high. Thank you for your help.