I have a brand new XR15, and it has a cover panel on that corner coveing the service ports and wiring. Its attached with screws that screw into those punched holes in your photo to the right of the louvered sheetmetal. I would imagine that yours should too. Funny thing is, every sketch in this manual shows it removed. http://www.munchsupply.com/UserFiles...ide%20XB14.pdf
Another manual: http://www.americancoolingandheating...fications1.pdf (Google is your friend, well maybe.)
It might be best to ask at HVAC-Talk.com by registering there and posting your question there.