Guest house tenant running A/C all day. What to do?

[Chris Park]

Guest house utilities are shared with main house under my name.  New tenant and he’s running the A/C all day and night even when he’s not there for long hours at a time

I’ve told him to be mindful and turn it off when he leaves but so far no help.  And he often turns it down to the low 60s

I do have an energy efficient home setup but this is ridiculous.  What can I do outside of charging him for the extra he’s using?

[Nathan Gesner]

Quote from @Chris Park:

Continue to remind him, but that's about all you can do.

In the future, consider adding a limit to included utilities. For example: 

"The monthly rent rate includes up to $150 in utility costs. Should Tenant use more than this amount in any given month, Landlord shall bill the excess charges to the Tenant. Tenant agrees to pay the additional amount the following month's rent payment."