I found a bare copper wire in my HVAC unit after service call. It shouldn't be left bare, should it?

Hello, HVAC.

TL;DR: When I decided to replace an HVAC control board myself, the technician who offered an estimate advised me to reverse the temporary rewiring he did on an earlier visit. When I opened the panel to do so according to his instructions, I found a bare copper wire in the bundle. It shouldn't be left bare, should it? Should this wire be connected to something, and if so, what?

Relevant imgur album:
http://imgur.com/a/rxGVb

Detail follows:

A few days ago, our unit was blowing hot air when it should have been blowing cold air. Yesterday a technician arrived and diagnosed the issue as a faulty control board. He committed to call us Monday (today) with a quote to replace the board. Also, he entered our crawlspace to modify the wiring under there somehow, and he may have jumped a wire using a wire nut in the outdoor unit enclosure. He said the change he made enables the cool air, but the unit will not blow hot air-- so it's a temporary workaround until he can get the new control board.

Today I got the quote: $382. So I decided to see if I could do it myself first, since the part is just $40 on Amazon and the process for replacing the board seems to be pretty straightforward.

I called the tech to ask him to come undo whatever changes he made-- I offered to pay for this second visit-- and instead, he said all I needed to do was open the enclosure's wiring panel, remove the orange wire from the yellow wire bundle's nut, and nut the orange wire together with the brown wire. Okay. Still, I wonder what wiring he did in my crawlspace.

When I opened the panel, I found this:
http://i.imgur.com/5cyuWIJ.jpg
The wiring is as he described, EXCEPT FOR THE BARE COPPER OF ONE OF THE WIRES. Should this have been left bare? Should it be connected to something? If so, exactly where should I connect it? To me this looks like a potential fire and safety hazard.

Also, if I connect the wiring according to his instructions when I replace the control board, will the resulting wiring be acceptable as a permanent solution?

Thanks for your help!

submitted by /u/nonsensepoem
[link] [comments]