Burgundy_Boat: The **** to control hot and cold is connected to a flapper/door that directs airflow. Check it for binding. If that is fine you may want to check the door to see if it is sticking. You didn't mention if the was harder to turn back to cold but if it is, then this is probably your problem. Unfortunately the only way to really fix the problem is to take apart the dash and look into the climate control passages. LOTS of work. My wifes GP has an automatic climate control but was blowing hot air when it should have been blowing cold....turns out the door/flapper got stuck and the climate control wasn't able to pull it free. Same principle here...just manual.
Jeffreyeffery: Going way back to 96 on this one...I had a similar problem with my automatic climate control...it was way out of whack. Since it was under warranty I brought it in and they replaced the thermisters (temperature sensors) both inside the car and outside. Don't remember which was the culprit but the computer uses the information from these temp sensors to determine what to provide (heat or AC). Not sure how to test them (don't know what the correct values/ranges should be) but they are easy and cheap to replace. That solved my problem.