I would use 10/3
Black and red to the breaker
White and bare or ground to the neutral bar
With a 2 pole 30 amp breaker
No need to paint wires
Plastic box is OK
Checking 220V put meter leads...
Check capacitor to fan... turn power off to condenser... pull electrical panel off condenser... should be a silver round or ovel can looking thing with wires going into the top side of it... this is...