Ok this is gunna sound bad because I am service mgr for chevy and have been for a long while. Anyway when my heater or a/c is on no matter what speed the fan is on after about 10 min. of the blower being on the air stops flowing out of all vents. Meaning defrost floor and dash. You can hear the air blowing but it's like it is trapped in the dash kinda like it looses vacuum and all the flaps close off or something. You can get it blowing again by either turning the air off and waiting a bit and turn it back on or play with the vent selector going from vent to defrost a cpl. times and it will blow out where ever the selector stops. I hope this makes sence anyone know how to fix it?

1997 blazer LS4 door 2 wheel drive 4.3L engine with automatic

 

Have you tested the vacuum supply to the HVAC control unit? I will see if I can find the control logic for some meaning to the testing of vacuum supply.

 

I hope you can find it cause the dealer ship I work for can't seem to get it and thanks for the reply

 

Well, here are the vacuum diagrams and component descriptions that I could find:


Looking at the schematic view, it looks like there is no doors which could completely block off the flow of air... Do you still hear the fan blowing? The is the time (10 minutes) a consistent value or does it change? If you select recirc, does the air flow improve?

 

yes you can still hear the fan blowing at all speeds. inside and outside the truck. 10 min. is a guesstimation sometimes its 20 min and sometimes it is before I get to the end of the street. Sometimes it does it while the truck is just running in the drive way to warm up the truck before i go anywhere. If you play with the dial for a bit you get air again or you can just turn it off for a bit then turn it back on and it is good again. It does this on recit. air or ousideair does not matter. Most of the time to get it to come back on I can put it on max air and wait a few and it will come on but when the outside temp is in the single digets every second seems like forever

 

Is this the thing that operates the temp control door? If it is, where is it on my blazer. http://info.rockauto.com/getimage/ge...04-100-001.jpg

 

Yep, that is it. It is located on top of the HVAC housing accessible with the glove box dropped down. There is a catch to the left side of the glove box door when open. Lift the catch and pull the glove box out and down. It is fun to get to. I hope you have a really, really short screw driver. The type that use a bit and a ratchet work.

 

mrafindley, have you checked to make sure that no debris has accumulated in the HVAC inlet in the cowl area? You will need to remove the screens above the firewall to check this.

 

Sounds like the same blend-door issue I have.

-sp

 

Ok, thanks, If I only have lukewarm air coming out all the time,both my heater hoses are hot, and the rest of the controls seem to do what they are suppose to, is this the part I should look at next? I already tried pulling all the fuses to reset everything. It was fluctuating back and forth between hot and cold air in the summer, now I just get lukewarm air all the time, so i don't think the core is clogged.