Air Conditioning - Buying a HVAC unit.

How does a home owner go about buying a central system for new construction?
Why? Well....
I can't get the guys to come out and work for more than a day installing but they seem to not mind service calls. I can install it and they can come out and charge it up from the looks of things.

Normally, the builder puts it out to bid or uses a contractor he's used before. Then it's a contracted job; no workee, no payee.
I take it you're building your own house?
Tom Beer 4U2

Yeah. I understand how the other guys do it. I was wondering, in the event my guy fell through, how I could go ahead with my work until the environmentally friendly part of it came up.

Turns out, after I posted my question, the guy called to come pick up his start-up check.

But if I wanted to rough-in my own, how would I find a dealer?

Oh yeah. That little beer looks good right about now. Pretty warm and dusty outside.

It sounds like the contractor has more than one iron in the fire, and is getting to the jobs on a schedule. Which is understandable. After all, one doesn't want to put all one's eggs in one basket, do one?:NO NO NO:
I, for one, will not encourage anyone to install their own system. That takes bread off my table...:PTB:
Tom Beer 4U2

I can appreciate that. It's the recent down-turn that woke me up and got me to start doing more for myself.
One can only ask.
Sometimes I find craftspeople comfortable enough in their skin that don't mind sharing. It comes back to them when I call again or do referrals. I know that doesn't help you from where I live.
It seems like all the people who come to me to get things planned end up calling me part way through the job to help.
I'll work it out. Main thing is I'm getting my work done. Although now it's getting hot and he'll be sweating more than last month.

It is true that a homeowner who does his own a/c work could cut into someone's income but that isn't why we do not support this advice.
It is purely because you must be certified and qualified to do this work and information gathered from forums does not qualify you.

You will find all manner of advice here that is in the realm of what a homeowner can do that will cut into any other trade's bread and butter.
Tradespeople are probably the biggest diy'ers out there which is why you find them here answering questions!:D