I want to add a bathroom with shower and sink, lay floor, insulate the walls, put in an air conditioner unit/heater, mini fridge, bed, etc to make a studio that is Covid safe for both tenant and landlord as a short term rental, AirBNB, or even long term since a popular college is about 15 minutes away. 

When faced with an option to make money the same way the bank does every month without being obligated to 2 am phone complaints about a stopped up toilet or broken air conditioner, it's usually a pretty easy transition to seller financing.

For one, I added a few touches; including adding 2 new Air Conditioners and a ceiling fan along with a new microwave and a single oven.

If they keep complaining and they have been good tenants consider lending them a window air conditioner to place in the bedroom.If they keep complaining and have been lousy tenants offer to let them out of the lease, repair the HVAC unit when parts are available and rent again at a higher rate.

I walked over and talked to them and they said their landlord wouldn't fix the air conditioner.

It is a single family 3/2 built in 2020 that will be cash flowing roughly $500 a month after all expenses.I would like to invest this money into an emergency fund just for this property and grow that fund to $10,000 before I start putting this $500/month into a different account.I want to prevent this emergency fund from being eaten up by inflation, while also protecting it from taxation in the event I have to withdraw for a big cost (ex new roof, air conditioner, etc)Could anyone recommend a good place to park this money?

I was tired of renting, in renting landlords were always counting on me to fix things as they broke air conditioner, water heater stove/oven leaky faucet... decided if I was gonna be a "handy man" I might as well own the property I'm fixing How did you find this deal and how did you negotiate it?

A heat pump is an air conditioner run in reverse.

So my recommendation would be to:Respond in writing - text or email - that you are committed to her having a working air conditioner for her trailer - especially in our hot and humid summer. 

They have to be vented out of the window but there is no danger of anything falling as your tenant stated. https://www.goodhousekeeping.com/appliances/g21286604/best-portable-air-conditioner/?