Heater Trouble, maybe vacuum

Hi I have done some extensive searching but have not found an answer to my problem. Which is that when i turn my vent control (99 cheorkee,4.0) to either windshield setting I hear a vent door slam, behind the radio i thin, and then the air basically goes nowhere, but behind the radio gets hot. If I turn off the heat/air, I can lower the fan speed and sometimes get it to the windshield on the 1st fan setting. For the record, my cursioe works great. Any ideas, it's 35 in MI and the windhshield takes forever to stop fogging/frosting. Thanks.

Sounds like a spring on the blend door came loose. Don't know how hard it is to get to though.
Good luck

I don't think this is the solution, as I have a lot of temperature control, the air cond. is cold and the heat is hot.

The problem I have is there is something that does not "hold" door open for the defrost vent. It literally slams shut, you can hear the air pressure cause this.

Does anyone have any type of solution for this? Thanks.

See if you can access the vacuum solenoids (solenoids?motors?) to the left of the vents. Not sure how the '97+ layout goes, but if it's anything like the earlier ones, you should at least be able to disconnect the vacuum connection and operate the vents by hand, by pulling or pushing on the linkages. On the '96, the frontmost solenoid controls the defroster vent.

The defroster plentum is directly behind the radio on the 97+. I would bet that the hoses to the defrost vents somehow came off, or maybe even the plentum itself came loose from the heater housing. You're going to have to remover the top of the dash to access it. My guess is the lack of air resistence is what is causing the defrost door to slam. Also the air blend door moter is electric not vacuum.

My mode doors are slow and make an audible 'pop' when it's even a little cool out.

I have found that if I change the setting, it's less stress on these cheesey little flaps if the fan is at the lowest speed.