Blend door issues. Please help...

[spinedoc]

My 98 Yukon has a heating problem. It always blows air from either the defroster or the dash, but never the floor. I checked what I think is the blend door motor, on the drivers side under the dash. It moves when i turn the blend knob on the dash, and when I remove the motor, I can manually move the door to all the positions.

Is there another door that deflects air to the floor I am missing? Any help would be appreciated.

Thanks

 

[SunlitComet]

there are two door cranks for the out put distribution. they are connected with linkages to the motor above the gas pedal on far left side of the hvac box. you really have to look up in the dash from below.it is considered to be the mode doors. the one you see on the rear of box by looking at it while leaning down a bit from the seat is the blend door or temperature control door. just to clarify which knob or you turning?

 

[spinedoc]

Sunlit, let me see if I can follow you.

I looked at the blend door motor, the one above the gas pedal. It moved with the 'zone' knob (the one that directs air to the defrost, panel or floor) and I saw the arm of the door move. It moved through it's range from stop to stop. I removed the motor and could also manually move the door through the range of motion.

With the key on and the fan on, I could move the door either with the motor attached or by hand, and I could get slight changes in air on the floor and panel, but the bulk of the air was still coming through the defrost vents.

I am not sure if there is a flaw in the dash controller computer, or maybe in another vent door somewhere in the dash?

I hope this will help to clarify the situation. I really appreciate the response and hope you can guide me through this.

 

[SunlitComet]

that "zone" knob and motor is generally called the mode knob and motor. the "blend" one is the temp control sub-system. on the mode motor did it move exactly as you turned the knob with out skipping or stopping during the whole range of knob motion? there is more then one door for that mode. did you adjust doors by turning the point where the motor drives it did you see both door cranks move?

 

[spinedoc]

I'm sorry, I think I may have been referring to them wrong. When I turned the zone knob, the door moved smoothly along the whole range. I was only looking at one crank. Are there two cranks attached to that zone/mode motor? Where is the other door that the zone/mode motor runs located?

Thank you

 

[SunlitComet]

look at parts 25-30 to give you an idea. as you see by the crank levers the two doors ar next to each other.

http://www.gmpartseast.com/chevy/co...ater-module-asm-tc090450109-l31m30k10706.html

 

[spinedoc]

I think I see what you mean. I will check that out tomorrow after work. Would one of those doors malfunctioning cause me to have most of the air come out of the defroster?

Thank you for your advice, I greatly appreciate it.

 

[SunlitComet]

yes.

 

[spinedoc]

Sorry for the delay. I looked at the truck and saw both arms moved through the complete ROM. I reached my hand up and saw that both doors I could reach moved smoothly. I then thought it may be the actual climate control computer board so I took it to a dealer.

They told me that the computer was fine and the problem was the top door, up near the defroster was jammed up. the told me it was a 5+ hour repair, plus parts.

I elected to take it home and try it myself. I found this thread..

http://www.thetruckstop.us/forum/th...t-door-hvac-flow-distribution-flap-box.31159/

which I think is what I need to do. Any advice, does this look correct to repair that door? I am a little overwhelmed by the looks of this, but I am going to try it.

 

[SunlitComet]

looks correct.