We had tenants ask for air con last Summer, she had just had a bub and we were having a really humid Qld Summer. We asked them to sign a longer lease (but no rent increase) as they were only on a 6 mth lease. They signed for 12 months and we put aircon in the living and the master bedroom. Everyone happy
Eta - degrassi, I think it's worth asking and I'd add that you would be willing to sign on a longer lease.