Good communication, very knowledgeable, and did clean high quality work (I'm a retired plumber and know what clean work looks like--there's a difference).
Most importantly, Jack is trustworthy. I know this for a fact because another HVAC contractor (from Thumbtack) came out and quoted me $1,800 for this same repair. The guy said my two year old air handler must be replaced, the lines needed to be acid washed, many many pounds of expensive coolant would be needed to charge the new system, etc. Basically, it was the typical scammer sales pitch contractors notoriously use to raise costs-- "everything is broken and must be replaced", when in reality, it's a simple fix. In stark contrast to this other contractor, Jack was honest and only replaced what truly needed replacing. He did the whole job for just $239! You read correctly: another Thumbtack contractor $1,800, Jack $239.
What's more, when it turned out my system needed an extra pound of coolant (not much), and it cost a little more than his original estimate (an estimate given sight unseen from email); Jack looked like someone ran over his puppy as he gave me the news. Clearly, this is a contractor who does not enjoy up-charging anyone. In a market filled is lazy scammers, it's refreshing to come across this young man who takes pride in his work and truly cares about giving people honest value.