Should I accommodate an air conditioner

[Missy H.]

I just bought a duplex rental property in Albany, NY.  It is an older house - early 1900's.  The previous owners had a PM company managing the house, but nothing was ever updated and any repairs were just a band-aid.  

I inherited tenants downstairs.  An older couple with a son in college.  They keep the place clean and pay the rent on time.  I just renovated the bathroom because it was terribly outdated with cracked tiles and water leaking into the basement and I am planning on re-building the porch because it is a potential safety hazard.  I also renovate the upstairs apartment with a new kitchen, paint and refinished hardwood floors to make ready as a rental.  

The son sent me a text the other day and said that when he turns on his air conditioner, the electricity goes out in the kitchen.  My question is:

Would you upgrade the electric to accommodate an air conditioner?

My first thought is to have an electrician go and take a look.  If it is a simple repair then I don't see a problem, but if the electrician tells me that it needs to be upgraded, my thought is what did they do the previous years before I bought the house.  The current electrical panel is 120/240 volt service with a 100 amp panel for each unit.  The home inspection report states that this is sufficient for each unit.

What would you do?