If you're taking out the glove box, you should also check the vacuum lines coming off the distribution block to the left of the glove box opening. While they mostly control routing of air to different vents, one of them controls a flap that mixes hot and cold air. If this is not working, it may be part of the problem. Should be the line attached to port #6.

Edit: you should check that the line holds vacuum, meaning that the part on the other end of the line still works.