You can only go to hill stations in South during summer. Because the heat is unbearable in South. You can go to Munnar in Kerala or Kodikanal in Tamilnadu is also a better option.
You can also check out Ooty and Connor hill stations in Tamilnadu.
You can visit a number of hillstations in South India during summers.
Ooty in Tamil Nadu
Kodaikanal in Tamil Nadu
Munnar in Kerala
Nandi hills in Karnataka
Yercaud in Tamil Nadu