Ok, not to beat a dead horse, but my '03 Screw has a problem directing heat to the floor vents. I have read the fix before in this forum but after reading thread for 2 hours I can't find it. Does anyone have the answer? It had something to do with the vacuum and or the flapper door?! Please help before I get served divorce papers. Thanks all!

 

The direction of the heater output is vacuum controlled. The default position (no vacuum) is to the defrost vents. This is for safety/visibility reasons.

So, if your heat goes up to the defroster vents, it usually indicates a vacuum leak somewhere. I think some have indicated that the most common place is at a vacuum line or reservoir under the hood, but, unless someone else posts specifics, you'll have to try "search" again.

 

99- i know how it works, but unfortunately i have not had mine open where i can give you specifics. == there is a vacuum line from the under hood area to the control panel for the heat- cold. the vacuum goes to both the "temp" **** and the "positon of heat" ****. if you can change the temp from HOT to COLD then you have a vacuum line connected to the panel. also i you can change the air from DEFROST to FLOOR, then you must have a hose with vacuum to the panel. if neither works, you probalby have a bad hose from under the hood area.--- if the HOT-COLD **** works, but you can not get it to the floor, then the mixing door cylinder (actuator) is stuck, or the hose fell off. i THINK, this is on top of the drive shaft hump, under the hood, behind a plastic panel near the floor. this should be under the heater core. i cant give the exact location;, but you should see a small air chlinder a coule inches in diameter and a couple inches long with a vacuum hose on one end. there should be a steel lever that stick out of the cylinder and thru the heater housing and connect to the mixing door. as you move the HOT-COLD ****, the little steel arm strokes the door. you can pull it manually and test also. if you find it, you can remove the hose and see if you get vacuum with engine on, and **** to "floor". i wish i could give more details, but last heater i look at was a 89 model.

 

the drive shaft hump, is inside the truck, under the dash ( not the hood), up aginst the firewall. look for some type of plastic panel protecting the heater core area.

 

Look between the battery and the firewall for the small line that runs through the firewall.

This line cracks and leaks and is the most common reason for the defrost-only airflow.

Steve