Pontiac: heater blowing cold air, pontiac bonneville sse, pontiac bonneville

Question
when I turn my heat on in my 93 pontiac bonneville SSE, or even when I start my car in the morning the digital temp lite starts flashing for about 25 to 30 seconds then stops. I change the termostat and thought that whould help but it don't. Chould I have a bad sensor or clug heater coil or something. If so can you tell me how to fix it please, it getting cold here in Indiana.
P.S. is it possible for me to run a self diatnosite test on my car.  
                           Thank you.
                           Sign: cold in Indiana

Answer
this one is NOT going to be easily diagnosed and reapired. You will need to have a professional automotive facility do this work for you. If it did NOT require special test equipment There is NOT much you can do as I am prety sure that you do NOT have the equipment.

Lemon-AID