You don’t get the “full warranty” when you DIY hvac installs. You also need to call a licensed hvac tech to charge your system if it doesn’t come precharged. Mini splits are easy and I would 1000% DIY. Big, attic mount blower units I would leave to the pros for so many reasons. That said my cousin installed a 21 SEER unit for $5k. I was quoted $35k for the same system (:

I haven't personally had need to do it (yet), but I know multiple people who got the EPA certification to be able to service their own equipment. It can be obtained by taking an online test.

https://www.epa.gov/section608/section-608-technician-certif...

given installation price vs system price, it's possible to trash old one and buy a new few times for a price of professional install.

mrcool also has ducted units that comes with precharged/vacuumed lines. very tempting as one of my hvacs lives on extended timeline and quote for a new one was $25k 2 years ago

I did a 2 ton central air heat pump myself last spring with precharged lines. It was under $4K delivered, I was quoted over $10K.

It was a little scary, I had not done something like that before but a little research and it all turned out fine and has been working well.