Greetings Jon E,
It seems the 1985.5 944 has a recurring flaw and my offer of advice to pass along to your mechanic/shop would be for you to print out all of the possible suggestions from June of 2003:
http://forums.pelicanparts.com/showthread.php?perpage=20&threadid=114053
Pay close attention to the Clarks-Garage links.
Since many shops/mechanics have no idea on how to fix a 23 year old 944, you can be prepared to pay for their education. I say this in the kindest manner because you may be able to save some money by doing a few tests yourself. Your post said it is freezing, a real hard time for trouble to happen.
Could you provide additional information on the car-improvements or recent work.
Welcome,
John_AZ