The best thing you can do is definitely Hire a local PE. But with a little investigation you can do some checking to get a better understanding of the roof structure.
A 27’ span is not all that long for the truss designer to have designed your Roof system to be clear span, IE no internal bearings!. BUT the HVAC being in the attic complicates matters a bit.
The engineering drawings if you didn’t toss them contains all the relative information to accomplish what you are wanting to do. If you still have them then you’re golden!
HVAC, take a look in the attic and see if these trusses are different in configuration than the rest. If the answer is no then you know that there is a good chance that they are dependent on that loading bearing wall. Check chord sizes and plate sizes on both sides of the HVAC, They may be larger.
Most truss companies will do one of two things, 1- make the HVAC truss with a 2x6 or greater BC or 2- leave the BC the same size and stack another chord in the center panel to strengthen that area for the additional load.
If you trusses are all 2x4 then you have additional problems, they were not designed to carry the HVAC at all!!!:shock:
Get a PE or if you know where the Trusses came from they truss co can take a look at it for you in most cases at no charge!! 
Jeff Whitley
W&W Truss Bldrs Inc.
www.wwtbi.com