I am about to embark on such a do-it-yourself air conditioner installation. I have done a lot of electro-mechanical work as a factory maintenance tech and I think I can do it. I have spent many hours watching YouTube videos and reading HVAC books. The main thing you must know is venting refrigerant to the atmosphere is illegal and immoral. If you think you need to do this then call for help. Don't damage the planet!
I have a two story house with separate ac units for upstairs and downstairs. I have had three different service companies look at my systems over the last few years and none of them were able to get them working satisfactorily. The last company that came out wanted $600 to recharge the refrigerant with no guarantee since I may have a leak in the system.
Knowing that that is a ridiculous price, I went to Amazon and ordered a manifold gauge set (professional one for $200) and a 25 lb canister of R410A refrigerant for $107. I also ordered an electronic leak detector for $22 and an IR Temp gun for $30. I recharged my system to the manufacturer's specs and it now cools better than it has in years. I have found no leaks and my pressures and temperatures are holding steady. So for about $350 I recharged both my systems and I barely used any refrigerant. I could recharge them both 10 more times with what I already have.
Now for phase 2: (not yet performed)
My units are 15 years old, so I am working on my replacement plan. At acdirect.com I can buy a complete 2.5 ton system (condenser unit, furnace, and evaporator) for $1700. I need two so that's a total of $3400. I am sure I'll need some misc fittings and such, but I have Home Depot for that. The refrigerant lines are still good (just copper pipe), so I am reusing them.
Now for the additional equipment I will need. I priced all of this stuff on Amazon and only selected equipment that has excellent reviews. Granted, it is low end equipment but it should do the job.
Vacuum pump $200, Recovery system $400, Recovery tank $90, Pipe sweating (soldering) stuff $100, Tank of nitrogen $100.
You need the recovery system to extract the refrigerant from the system. The refrigerant can be reused.
I have done electrical work, so the electrical hook up should be easy.
The hard part for me is just mounting the furnace and evaporator in the attic. Although, I don't anticipate any big issues.
Next I will fit all of the pipes together and pressurize the system with nitrogen prior to sweating the connections. The nitrogen helps keep it uncontaminated on the inside. It is okay to vent the nitrogen when you are done since our air is mostly nitrogen anyway. I am buying some extra copper pipe so I can practice soldering it ahead of time. I am new at this.
After soldering the connections I will connect the vacuum pump and evacuate the system. You cannot have any air or moisture in the system prior to charging. If the vacuum holds and I have no leaks, all that is left do to is charge it with refrigerant.
So I have spent $3400 for two new systems, and about $1000 for tools and equipment that I can use to maintain and troubleshoot my systems in the future.
Church Services in Round Rock, TX quoted me $22,600 to replace both units.
What could possibly go wrong?