I hesitate to reply as the post is so old but to get to the HVAC motor on the 350SDL (1991) take off the under dash carpet and the sidewall panel on passenger side. There on the right side about 3 inches up you will see a black pipe and the motor in a flexible aluminum holder wrapped in foam. Unplug from the rear and replace. No need to take out glove box or vents as they will not help you get to this little PITA.