Heater and or Vent issue

2001 Dodge Grand Caravan Sport: Mileage 62000
I seem to have a issue with my heater and or the vents. I have hot air blowing out of my driver side vents and cold air out of my passenger side vents, even though the heat is turned all the way up on the passenger side to. I tried all the compartment settings and they all seem to be the same way. When I change the location for the air to the top of the dash which should be combined, all I feel is cold air for the most part. I had my water pump replaced no more than 4 months ago, could that be the issue? My fan blows nice and strong, so no issue with that. I asked a guy at Fletcher's Automotive yesterday about the problem, because they are the ones that did the repair work for the water pump and he said it was probably some sort of switch in the dashboard that opens and closes the vents. He wanted to charge me $80 to estimate the problem. Help!

If you have any ideas please let me know. Thank you.