Ventilators, would it be possible to build ventilators out of HVAC equipment or shop vacuums?

You need to control the pressure and/or volume of air. If you don't, you cause more problems by rupturing the lungs. In theory, you could if you can control the above, but it will be much more involved than just hooking up the output of a shop vac to someone's mouth.

Let's hook you up to a 12,000 cfm HV unit and see what happens.  If you even knew what a ventilator is you wouldn't be asking this question.

no, easier to build them from scratch

Dison is already building ventilators.