Hi Scott,
You can absolutely rely on the tools. It is 100% accurate. The problem was that you are tracking a specific subdomain and your ranking for that keyword is not in that subdomain.
You could resetup the campaign as a root domain campaign as a catch all. That will get you anything off of that domain regardless of whether it's www, blog, store, or whatever.
I know it's frustrating and seeing your ranking suddenly drop off can be worrisome to say the least.
What you can do in the immediate is to set a 301 redirect from http://ssihvac.com to http://www.ssihvac.com and once Google catches up with that, you'll likely see your ranking position returned to the www without having to archive your campaign or anything like that.
You really don't want the www and non-www to resolve independently anyway, so that's something I recommend in general anyway.
I hope that helps.
Cheers,
Joel.