rtparr.... thank you very much. I knew that there had to be a sensor somewhere in the return system to tell the EEC when temp had been achieved, but had no idea where it could be. The previous owner of this lovely car had it well serviced, but it was absolutely filthy inside and out. It has cleaned up beautifully, but she was a heavy smoker, and the interior showed it. It just struck me that in cleaning everything, including the ductwork, I had never come across anything that struck me as a sensor. The accumulation of debris was incredible. I would have never found it on my own. Thank you again for your help.