Whitewinghunter, I took your advice and decided to replace the control box. While I was trying to make sure I had the correct A/C model number, I discovered that the control box and thermostat that were installed on the unit we not correct. The box and thermostat were designed for a unit with a heat pump, when in fact the unit did not have a heat pump. I ordered the correct box and thermostat, installed it, and now it works properly. Thanks for the suggestion.