My heater switch to control my vent options don't work for floor heat?

I have a 2002 sanoma 4x4, and am having problems with my heater not working on floor vent mode. I have tried almost everything in testing the vacuum lines. How I tested was disconnecting the heater and removing the group of vacuum lines from rear of the vent selection ****. I then start the truck to get suction from the main vacuum hose and use a jumper hose to complete the connection and actuate the various vent settings. I have even used a large jumper hose to try and test the vacuum pot down near the drivers gas pedal which has a red and a blue hose connected to it. In the end I am able to actuate all other vents but not the floor vents. Can you lead me in to the right direct to solving this problem.