Cooling issues on the top floor - HVAC issue

[Greg S.]

Hello, I bought my first rental property in December of 2016. It is a 3 story townhouse here in the Baltimore area built around 1900. I am having issues with the A/C cooling the entire house. The 3rd floor is noticeably warmer than the 2nd and 1st floors. The thermostat is on the 2nd floor and is set to 72. On days where highs are in the 90's and lows are in the 80's, the 3rd floor is about 8-10 degrees warmer than the 2nd floor. Also even the 2nd floor has been only getting down to 76 when the thermostat is set to 72.

The A/C unit is 17 years old. One month ago I had the Freon charged as the levels were low hoping that this would get the unit through the summer. It still has not been able to cool the house adequately. 

I am looking for advice on figuring out why the 3rd floor is noticeably hotter than the 2nd floor. Is replacing the unit with a larger one the best option here since I already had this unit charged/had the coil cleaned?

Thank you