A/C blows cold only in max ac setting, reg ac mode blows hot

What is your question?

The heater works fine. The a/c however only works in max a/c setting as it blows quite cold. As soon as I set it down to normal a/c setting with the dial still in the blue cold area.. it immediately Begins to blow hot air. Not even the ambient temp. I just purchased the 1997 B4000 4.0 two days ago and am still familiarizing myself with it. My guess is a HVAC control module or door/flap? ? Ideas greatly appreciated.. Thanks