code violaton?

I had a company install a fixed office system over my hvac unit, now I can not get to shut it off/on. Is this a code violation? Is there a violation of obstruction a vent? Should there be a clearance height?

That is more an electronics question.
I doubt it is a code violation ,but may be a common sense violation if duct is not insulated and gets very hot .

There is only one way to determine a “code violation” and that is from the only source authorized to make such a determination…the authority having jurisdiction in your particular area.

There are a variety of sources that suggest proper installation and, upon their adoption by cities and counties, modifications can be made by ordinance/law and interpretations can be (at best) inconsistent and (at worse) wrong.

But the AHJ is right even when he is wrong, according to the law…unless overturned by appeal.

Start with your local City Hall and learn what your code book says on the issue…and start from there.

Good luck.