1991 Suburban Defroster problem


Old 01-16-08, 10:39 PM
Thread Starter
Join Date: Dec 2007
Location: Wisconsin
Posts: 14
1991 Suburban Defroster problem

I have a 1991 Chevy Suburban 1500 and need to get my defrosters working.
My fan motor is working great with nice heat and air flow.
Problem is I can't adjust air flow to the defroster, the floor, or even the a/c.
It is just stuck in one position.
I Haven't been able to use it much since this happened because the interior fogs up and then frosts up too bad and literally have to use an ice scraper on inside sometimes.

I have the dash about half torn out and it looks to me like there is a series of vacuum lines that should open and close certain vents when the lever is slid back and forth.

There isn't anything staring out at me saying "Here I am, I'm your problem"!

Can anybody try and walk me through this desperately needed fix????

Rob in Wisconsin
Go Pack Go!!!
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Old 01-17-08, 03:23 AM
Join Date: Jan 2006
Location: Owen Sound Ontario Canada
Posts: 541
Check to see if the flap is getting the signal

Can you hear the air trying to change the direction of the flap?
I had a Suburban that had that problem and it was a broken flap.
I took off the end where the air came out the bottom near the driveshaft tunnel and was able the grab the flap with my fingers and wedge a screwdriver in there to keep the flap on defrost untill I got another unit.
Might not be your problem but mine was a 1988. Close to what you got.
Old 01-17-08, 03:10 PM
Thread Starter
Join Date: Dec 2007
Location: Wisconsin
Posts: 14
Defroster problems

Thanks for getting back to me.

I'll have to go fishing around and see if I can find a flap.

Seems like there should be something like that, when you slide the lever, a flap should close so the air goes through the defroster lines.
But nothing else changes either, like the a/c, or to just have the air come out the middle vents and not the floor or defrost.

I'll give it another good lookover and post what I find, if anything.

Old 01-17-08, 03:57 PM
Join Date: Jan 2006
Location: Ontario, Canada
Posts: 759
On the back of your control where all the vacuum lines are, check to see if there isn't one line, larger than the others. When/ if you find it, pull it off & see if you have vacuum there with vehicle running. There has to be at least one feed/suction, to the control, and the rest get vacuum according to setting. If it can't be found, try to follow lines with a flashlight or something, to see if one heads in a little different direction, toward driver side, or through firewall, and the rest will most likely head toward passenger side. When you have it isolated, pull it off & listen for the "Hiss", indicating vacuum that far. If none, check at rear of engine on firewall and see if you can locate the vacuum line coming through, and follow it to its source. If you have vacuum at main line in to control, check rest of lines for vacuum when switched to different positions. At least one other line at each setting, should have vacuum present, if none, your control is probably buggered.
Old 01-18-08, 11:49 AM
Thread Starter
Join Date: Dec 2007
Location: Wisconsin
Posts: 14
Vacuum lines

Thanks Mike,

That makes more sense because there is no change on any of the other settings.
It's too damn cold out to do anything now. Temps are only going to get to zero if were lucky.
I'll wait 'til it warms up to around freezing.
I'll make sure and let you know what I find.
Thanks again Mike

Rob in Wisconsin
Go Pack Go!!

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