COLEMAN MACH 15 AC PROBLEM

SO MY COLEMAN MACH 15 AC IN MY CLASS C WILL NOT WORK ON COOL HIGH AND WHEN I SWITCH IT TO FAN ONLY IT WILL NOT WORK ALSO .IT WILL WORK FINE ON COOL LOW AND THE FURNACE WORKS .I REPLACED THE THEROMOSTAT BUT STILL SAME PROBLEM .SOMETIMES I CAN HEAR THE COMPRESSOR RUNNING ON HIGH BUT NO FAN .ANY THOUGHTS THANK YOU!