If you are KZN based the link to the MCSA KZN ice crags outlined in the RDs that Ghaznavid posted is probably the first to hit. Gauteng based ice climbers focus more on the Lesoto side (see the ice section of the Lesotho part of the wiki at
http://www.climbing.co.za/wiki/index.php?title=Lesotho).
In term of predictable conditions there are both Gauteng and KZN based ice climbing regulars that have been climbing every year for at least a decade (some for longer) without fail. Some ice seasons are better than others, but you can bet to see the regulars at the ice crags on just about any July weekend regardless of the temperature in Johannesburg / Durban.
If you are not an ice climber take the same approach that many on this forum have recommended for trad: join up with someone that can show you the ropes and help you discover the peculiarities of the various crags. The MCSA (KZN/Johannesburg) ice meets (look for their meet programmes) are a good starting place especially if you have little or no gear / experience.