2001 Jimmy heater problems

Hey,
Anyone have a 01 jimmy where the heat only goes to the defroster or dash but will not go to the floor? For the past 2 months when you put it on the floor it would go back and forth with the defrost vent when going up and down hills? Thanks for the help.

My '96 had a similar problem. It turned out to be a vacume problem since the whole HVAC selector system runs off of that. Check all of you vacume lines under the hood. I found a pinched line under the plastic cover on the left side of the fire wall leading up to the vacume canister mounted on the inside of the hood. Hope this helps.

I have just now found time to tear into this thing. I did check vacume lines and diaphrams to make sure they are moving properly. Then I found it the door that diverts the air to the floor is broken inside as the end that sticks out flops around. It also looks like this requires pulling the entire dash? Thanks for the help.