You need votage readings.
R & C = ?
Y & C = ?
G & C = ?
Make sure door interlock is pushed in when checking voltage. IF you have power at R & C but not on Y or G check your T-stat. Make sure T-stat is calling for cooling. I know you checked voltage on old board but you need to check new one. The...
Bleed each loop separatly keeping shut offs closed after bleeding. Bring loops online one at a time. Let each loop run for awhile before bringing another loop online.
2x4 above ceiling between trusses. Drill 3/4 hole in ceiling. install a piece of 3/4 emt with one bolt in door track and two bolt thru 2x4 above ceiling. did mine ten years ago this way and is a much cleaner install.