1998 Z71 - - no defrost

[DenisMcG]

My '98 GMC Z71 does no blow air from the defrost vents. All other modes work fine. I can hear things the rods etc moving when I move the switch to defrost, but I get no air from the vents (the fan is blowing full). I do get a little air from the floor vents (in defrost mode) so it seems that the flaps are not moving fully. I looked under the dash and see rods moving, but I am not sure which one is for the defrost vents. Any help would be appreciated.

 

PS. I just bought this truck, so I don't know if it ever worked.

 

Denis

[mcreyaufmiller]

I would check either the flapper doors or the controls. Yours should be electronic, not vacuum controled.

[DenisMcG]

Mike: Thanks for the reply, the problem was indeed the flapper for the defrost. It had gotten jammed and was not moving. I freed the flapper and lubed everything up. All modes work fine now.

 

Now I have to figure out what a mysterious switch under the dash does.

 

Thanks,

 

Denis

[kewlgye]

I've got a similar problem with my truck. When I go to turn my A/C on (with it coming out of the front vents) it blows, but you can tell the air is blocked off like the flapper isn't opening. Then I have to turn it to heat for a minute, and then it usually opens and I turn it back to cold. I've replaced that little electric motor at the bottom that controls most of the flappers, but it still sticks. I looked at the flapper door at the bottom, and it had a carmel color sticky substance on it, so I cleaned it off, but it didn't help. It looks like someone may have spilled soda down the vent near the cupholder and it's causing the flapper door to the front vents to stick closed. Does anyone know where this flapper door to the front vents is? It's never a problem when I want heat, but it is when I want A/C, it's getting very annoying. I've also lubricated the joints and such near that motor and on the bottom flapper, but I'm convinced that the problem is at another flapper door that I cannot find.