More info from yesterday post after another evening of research. Dual zone HVAC system, with MST damper controls and Amana control panel. Both zone dampers are wired the same way, both get 24V from transformer but zone 2 damper doesn't open when zone 2 thermostat calls for heat/cooling. If I short terminal 4 and 5 per instructions, damper will begin to move, but rather than stop at full open, it continues back to closed. In other words, the motor rotates the damper arm 360 degrees rather than the 180 degrees where it should stop. Replaced MST motor panel with new Honeywell exact replacement but still have same issue. Any ideas where to look now? Thanks.