Dart "Cool Aire" A/C

Almost impossible to say without knowing exactly what you have now. Some of these add--on systems are as simple as

a blower switch, probably multi speed. You may have or need a blower resistor for low speed

a switch to control the compressor, with a cap tube thermostat

possibly a low pressure cutout switch on the low side of the system, which simply goes in series with the clutch.