Hello and
. We are glad to have you join us here and we look forward to reading of your adventures and experiences. I am sure you will enjoy the website and forums. Good luck stay safe and keep us posted.
Assuming you have checked the fuse feeding the roof unit(s) and it is good.
Try the easiest to get to, first. Remove T'stat from base on wall by prying at the bottom tab, pulling bottom away from wall and unplug the data cable. if you see any corrosion, it will need to be cleaned up. Re-connect the data cable and turn it on. If you still do not get it to at least light up, the next step is to check the control board on the unit. Turn off 120 vac to air conditioners. You will need to get on the roof and remove the cowling or shroud off the unit. Remove the access cover (about 5"x6") to the control board. Inspect and clean the data cable connections at this end as well. check the fuse to be sure it is good and that you indeed have 12 vdc feeding it. turn on the T'stat. If it does
not come on you can take it up on the roof to one of the units and plug it into the control board through a phone line and through the data cable coupler . It must go through the coupler to the board. turn it on. If it lights up you have a data cable issue. If not, you may have a bad T'stat or control board. Let us know what you find up to this point and we an go from here if we need to but hopefully it is just a bad connection at the T'stat.