I guess it goes here...

[Sepiroth]

Hey all, looking for some help here. I got a 98 GMC Ext Cab Z71. I'm having a couple issues and I would like to get some opinions or maybe a been there done that and it fixed it.

Anyhow, the blower motor only works on High. Without doing any sort of testing, I'm guessing its the blower motor resistor, which from what I have read here, YAYY!!, lol

The second, among others quirks, is that on any vent setting, the air/heat is coming from mostly the Defrost and not where the setting is. For instance, if the setting is on vent, I'll get minimum circulation from there and a whole lot from the defrost. Any help there??

 

[Sepiroth]

So, noone knows??

 

[gmcyukondriver]

I've had fan control issues, but mine were the opposite of what you have, everything BUT high was working. I think it was the switch or something, never really looked into it because one day it just started working, and I haven't had a problem since.

I haven't had issues with the defroster, but I have seen threads about it. When I switch between defroster and cabin air outlets, you can hear a door move inside the dash. That door will close off the path to the area you aren't using, so it will sent air to where you want it to go. Yours could either be stuck, or the motor has issues. here are the threads I could find on it. Good luck! Like I said, haven't had to mess with mine, so I don't know much about it.
http://www.gmt400.com/forum/showthread.php?2292-Defrost-blend-door-keeps-falling-out
http://www.gmt400.com/forum/showthread.php?1999-knocking-noise-from-dash

Not exactly sure that's your problem, but it gives you a place to start looking, hope that helps.

 

[Sepiroth]

Thank you.