You could have also picked up a used unit via this junkyard database. I did this when my buttons were sticking badly:
http://www.car-part.com
Also, I wouldn't be surprised if the problem is your blower motor. Thus, Possibly, the brushes are worn down. Hitting the dash where you did or slamming the door might be enough to jar things back together. There are some for sale on ebay right now for your vehicle, or you can by a repair kit with instructions here:
http://www.**************.com
specifically here:
http://www.**************.com/store/item.php?item=126%20Heater%20Motor%20Repair%20Kit
Whatever you do, do not let your repair guy return your old heater controller until you are sure that it was the problem.