Visual/External improvement need to happen right away to increase the appeal of the property and attract higher quality renters: Landscaping, Power/pressure washing the exterior.

The fan is creating negative air pressure in the house so the question would be where is the air coming back in the house.

If it's a solid concrete pad, there is some new product (like expanding foam) that they can shoot in under pressure and raise it up a couple of inches.

I have a townhouse with a 20+ year old air conditioner and furnace.

Not only do you have eviction pressure, the tenant has the same pressure to do well by you because he not only doesn't want to get evicted, he doesn't want word to travel back to the company that he's a lousy tenant that disrespects his colleagues.That being said, how closely do you work with this colleague? 

One air-conditioning units needs replaced.

Besides the central air unit needing to be replaced at some point, the home is in pretty good condition...especially for the price in Houma, LA (notorious for expensive real estate) e.g. my home is a 2/2 @ 1100sf and appraises at $147k.But on the positive side, rentals don't stay on the market very long...most are taken within a week or two.  

First thing is relax and don't place any pressure on yourself. 

Even as construction increases and vacancies go up, the continued influx of well-educated young professionals may mitigate concerns about supply-side pressures.

Only problem is our bathroom water pressure is horrid.