There's clearly a lot of criticism in this thread about hiring contractors and what to expect. But what can we learn from this experience? Here's are two of my takeaways:
Whenever hiring a contractor, you need a detailed scope of work before agreeing on a price. The scope of work in this situation probably should have stated whether or not all materials were included in the job by the homeowner or if the contractor was providing some of the materials.
It's important to have an understanding of what a job should cost. A lot of people are stating that $250 is a ridiculously low price for installing an HVAC unit. This is obviously going to vary based on the type of unit. If it's a through-the-wall PTAC, then $250 is not ridiculous at all to replace an existing unit. That wouldn't take more than a few hours. If it's a whole-home air handler and condenser, then clearly $250 is way too low. The scope of work should state the type and size of the units being installed to avoid any confusion. If you have a basic understanding of the work that is required, it will allow you to understand when a contractor's bid is unrealistically low.
Anyway - just my two cents.