I have a Honeywell Universal MiniZone AC unit that operates with a unit in the attic and a heat pump outside; the system is about 10 years old. As of late, the unit would turn on and blow, but it wouldn't get cool. So we cleaned and replaced the filter, and that didn't work. I called an AC guy, and he said two parts needed to be replaced in the heatpump. So he replaced those parts... now, the unit won't come on at all. Now, he says I have an issue with the electrical control panel in the attic. I looked at it for myself and the "purge" light is flashing yellow. According to the manual, that means there is a ZMS sensor failure... But he is recommending I replace the entire board and not just the sensor. I'm not sure if I trust him now because at least the thing would blow before he started "repairing" it. I can't find anything on troubleshooting the purge issue in the owner's manual. Would you recommend I replace the entire board? Or is there a way to troubleshoot the existing one. What other issue could be causing this?