A/C Problem; smoke comes out from the A/C Heater Control Unit
 

My A/C only blows cold if I turn on the defroster. Then after about 3 minutes, smoke starts to come out from behind the A/C Heater Control Unit. Do I have a bad A/C Control Unit or could there be something else wrong? It smells like a burned electrical smell. My A/C does not blow cold even when the snowflake button is pushed in, only when I hit the defrost button does the compressor engage. I hardwired the compressor to make sure it kicks on and it did. I replace the A/C Relay and that wasn't it. I think I need a control unit, but am afraid to fork out the money and have it not be the right fix.