Programs to use for making drawings

Question

I am working on the HVAC section of the building for my project and was wondering which program we could use to draw the diagrams because one of the links you provided are dead and the other has a questionable download that I'd rather not try.  Could I use Auto CAD for this section? Thank you.

Response:

We don't care what program you use.  I used Google Draw in class.  Autocad is fine, though a program with variable line widths usually "reads" better.

Here's a fine resource for many free programs.  For diagrams I'm particularly impressed with draw.io.