Just to add to some of the excellent points that have already been made (AC, grow OP, Etc) you might want to go with LED lighting throughout the home if you are going to continue to pay the utilities and as @Colleen F. said get a digital thermostat that you can set minimum and maximum temperatures on. The LED lights are a little more expensive up front but they produce minimal heat, use much less electricity, and last a very long time.
Other things to consider is maybe going to the RUBS (Ratio Utility Billing System) system if that is legal in your state. This puts the payment of utilities back onto the tenant. Of course this wouldn't be able to be implemented until you start new leases.
I would also do a unit inspection, there is no need to give a reason as long as you give them your states mandatory warning ahead of time.
I know the LED's and Thermostat are a big hit at one time but they are both durable items that will save you enough money in the long run to pay for themselves many times over.