Defrost help for 1983 Blazer 305 A/C

[lomarrius]

Hi;

I need to get the defrost working on my '83 Blazer so that it will pass safety certification up here in Canada.

The heater and heater motor works fine, and the lower vents blow hot air. When the selector is set to "Defrost" (the vents on the upper dash near the windshield), no air blows through them.

I thought I would ask here to see if anyone had a similar problem.

I am planning to take the upper dash out of the truck to see if I can investigate the problem. Could one of the ducts have been kicked off? Or maybe it is plugged up? Is this fixable by a diy-er?

A mechanic friend said it may have something to do with the A/C on the truck having dust accumulation?

Any ideas would be greatly appreciated.

I have the service manual for the truck but it doesn't go into the venting/heating system.

Thanks.

[Blazin]

Look for disconected vacume hoses under the dash.

[78rustbucket]

just fixed this same thing on my 84. take off the vent cover that goes to the dash n defroster vents ( the one right behind the underdash interior light) theres a white plastic clip that hold the flapper door rod that may be broken n only allowing dash vents and floor vent to work.

[chevyfan]

i have the same problem so i had to wire my floor vent closed and it forced all the air out of the defrost vents. Where is the control panel suppose to get vaccum from? none of the heater selections work so i dont think that it is getting any vaccum. It has been like this since i bought the truck but never bothered me till it started getting cold.