As stated.....
Seal it up with A/C Foil Tape
Return side (warm) and discharge side(cold) should not mix
That 'copper thingy' is the air temp sensor for the panel mounted thermostat
not a 'freeze probe'
Ceiling grille....
2 sheet metal screws in 'return'
8 wood screws ---2/each side
That will expose the metal ceiling template
The 'black' divider block in rear appears to be one row too tall
(divider block is trimmed to fit----then slides into channel on template when template is installed)
With it a bit too tall the ceiling template is not being pulled up TIGHT against the foam seal allow cold air to leak over into return side
4 Mounting bolts hold template to ceiling AND A/C Unit to roof
Pgs 8 - 11
http://www.dyersonline.com/downloadfile/download/aitfile/aitfile_id/2562/
