All ducts and electrical are in placeMy budget is around 6kPlease help me get an idea of cost, best brands or share referrals for HVAC contractors.A bit of research shows that the equipment needed including compressor, furnace, tubes, etc comes to around 3k.

i am new to the forum but watch bigger pocket you tube since 2 years.I have 5 properties, all single family homes, Houston area, 4 occupied (only 1 has a mortgage,80%), 1 i occupy myself (mortgage80%)I am a real estate agent, single mom, running a small business that produces very good income of what i save about 60%.

The cover stays on for daily use, but the slot in the bottom needs to be open and the main drain at the bottom as well as the overflow tube needs to be clear.If the tub drain is slow, that needs to be addressed too, because its one system top drain and bottom drain as you can see from the illustration.Another thing is some people take the cover off and flip the slot side up so the water is deeper.

Check out You tube videos with Mark Kohler on this topic.  

Aluminium wiringBut another big one is "Knob & Tube Wiring". 

Lowest mortgage in the country AND his porn comment got him 200 upvotes & counting which must be some kind of BP recordhttps://www.biggerpockets.com/forums/530/topics/704333-found-adult-videos-shot-in-and-outside-our-portland-airbnb

First of all I want to say the podcasts and you tube videos have brought me here and I can't wait to become part of this community! 

You tube and john Highman are great place to learn about commercial real estate.

Connecting the outside condenser to the inside head unit is a small diameter tube with heat transfer fluid (pretty much antifreeze, IIRC). 

It's only an issue if you have knob-and-tube wiring from the 1800s, which you likely don't.