What can i do to fix it ?

i have a problem with my air conditioning if it running everything its ok but it is off this smell like dead animal comes out of it specially if it gets hot inside the house, i think this is making everybody sick in my house and this worries me, everyone is coughing my house and my kid has bronchitis i think i do too and my wife its on her way to it can someone tell me what it is and how to fix it