I can't believe that you can't. When I first read your title I thought this would be about a HVAC guy wanting to do electrical work outside of the HVAC equipment. That would be something that in most places is prohibited.
I used to tell the HVAC guys they couldn't touch anything on the line side of where the power terminates to their equipment. I don't think there is any issue with an electrician working on the electrical innards of the equipment