Central cooling worth installing in Tacoma?

[Blair Nye]

I'm house hacking a duplex in Tacoma, and like many homes in the area, it has central heating but not cooling. The summers seem to be getting hotter and there have been multiple miserably hot days in the house. I'm thinking that installing an HVAC or heat pump would be worth the cost in terms of comfort and resale value but am not sure. Anyone know if adding an HVAC or heat pump is worth it from an ROI perspective?

If I do it, I'll likely do it during the winter when there's better deals on AC units. Any input would be greatly appreciated.