I have been debating on what a tenant would value more between a new nice kitchen or central air conditioning.

This gives you breathing room and flexibility to find a buyer, with less pressure.  

Here is an example:Find a deal at 50-60% of ARV, tie it up, utilize equity in another asset as a collateral assignment temporarily, spend 2-5% of ARV to fix up or retenant the property, then receive up to 75% of ARV back (cash out refinance) thereby "netting," you cash back ,  allowing you to acquire a property, and provide you cash flow (depending on your market).This would be a 0% down deal or negative down deal since you're getting cash back up to 75% of ARV.Yes you need collateral but, not necessarily since a more experienced individual with collateral or high net worth person could assign collateral on your behalf (perhaps a mentor).So by combining creative techniques, your own or assets of others, deal finding ability, and knowledge of the banking products and how to converse with bankers you could create and print money out of thin air (well you do have to invest your time of course).

It is one thing if you have a building inspection which uncovers something major and return to negotiate a remedy, it is quite another to put pressure to lower the price simply because you offered an amount over your comfort threshold.  

I see some price pressure from the fact that wages are not growing.

Originally posted by @Dawn Anastasi:The HVAC contractor also was wondering if I wanted to add central air, as it's not supposed to be "that much more". 

The concern I had was the fumes soaking into the porous wood and subsequently returning to the air for the occupants of the home to breathe.

I wouldn't smoke test until exhausting other options first; sewer pipes rarely crack inside a house unless someone has damaged it, because they're not under pressure.

I recently bought a new duplex and it came with two new central air units.

Air mattresses and 5 gallon buckets are a cheap solution.Then for the staging in the living room, I would pull the chairs and couch facing one another so it seems to be more of a conversation area.