Some time back, perhaps last year I purchased a used ATC control head on ebay due to an intermittent "no display"on the original unit. Recently the AC seemed to not be cooling as well as it had before. Previously I replaced the evaporator and it was cooling very well, only the display did not come on at times. The replacement ATC control worked well until recently. I checked the refrigerant charge and it seemed to be ok. Previously, when it acted up I found some info from a Mitchell Manual at a local library and I performed the recalibration/diagnostic test according to the directions in the manual. After that it would show a code 23 which is Blend Door Actuator Feedback Failure. None the less the AC worked fine after that. So, I attempted several times to enter the recalibration & DTC check mode, but was unsuccessful. I pressed the floor, mix, and front defroster buttons at the same time after I made sure the temp reading was 75 and the fan speed control counterclockwise to off, engine on, transmission in Park. I need to know if I need to get another ATC control head or is there something else I need to check first. Thanks, DaveC.