I've had this problem since I got the car 4 months ago. (1986 Trans Am 305TPI) Every time after the car is warmed up I put it on defrost to get the window defogged. Then I put it on vent but the air stays on the defrost even though I have it on something else besides defrost.

And one more thing is wrong every time I put on defrost right on start up snow come in through the defrost vent. Then I put on the windsheild wipers and more come through. Its like the windsheild wiper are pushing snow in through the vent. I don't know but it is making me mad and I am tired of being cold at 5 in the morning going to school.


Any ideas what to do

Please Help

Thanks

 

as for your malfunctioning switch, my 89 does this and all i do is kinda whip over that selection and it does what i want it to. the contacts might be dirty is why its not responding properly.
as for the snow coming in, all i can think of is your glass isnt sealed well or its being shoved thru the HVAC hump in the engine bay and its being blwn thru the system. id try and get that fixed as it might cause other hidden issues.

 

Check the tree at the back of the intake you should have several little vacum hoses goin into it, this controls your vents in the air ducts that makes the air come out the feet vents or defrost. If any of those hoses are rotted it will keep the air from blowing where u want it, As for the snow coming in check your system out make sure you havent got any holes.

 

Defrost is the default. You have a vac leak somewhere. Put your ear to the HAVC and listen. If you hear a hiss, you'll probably need to replace the vac control valve.

https://www.thirdgen.org/forums/atta...duct010707.jpg

JamesC

 

James, is that a common part store part or is that a dealer item? also, when replacing it, do you pop off the lil lines and cross them over or do you cut and splice?

 

Dealer, I believe (or GMPartsDirect. I "believe" this is what you need: Valve Vac Sel GM part # 16032395). The piece in question has arrows in blue in the above link. You remove the lines, replace the valve, and replace the lines--no cutting or splicing.

JamesC

 

kool deal. i have a union auto parts that sells delco stuff and i'll give thim a swing, dunno why i didnt think of that when i was typing.
another PN for me to put in my file

 

Ok how hard is it to remove this HVAC control I'm afraid I might break some thing when I just want to check it. I am still driving the car now and it is cold out there. I dont want to freeze from no heat eventhough it is the defrost and is draining gas.

So what to do JamesC you sound like my got to guy for this for now

 

Don't know if it's the same for your Firebird, but on my IROC it's literally six screws. Three hold the faceplate on, and three more hold the controls themselves.

 

I have 4 screws to hold the controls module in place but thats pretty much it. The 2 places where the screws on the right side go are broken so the faceplate hold the module from hanging. But I want to know how to get the hoses off without breaking them off. Then just put it back on after changing it. So if theres another pic to show what you mean by taking it out

JamesC good pic of the unit BTW

 

Like Aaron I'm unfamiliar with Firebirds. If yours is similar to Camaros, once the mounting screws are removed, you should be able to pull the HAVC out far enough to at least see (and perhaps remove) the vac harness. I can't recall exactly how the harness is held in place: either push-on type retainers or two small bolts. The HAVC at this point will be held in place by the slider control wire.

JamesC

 

IIRC, the vacuum harness has screws, and the wiring harness has a couple plastic clips. You will also have the lights to contend with. I've read that Pontiac used more than one light, but I've never checked.

 

Sounds like there is a hiss coming from the passenger side under the hood right by the firewall

So what would that be if it is something

 

That's approximately where the vac line enters the car.

JamesC

 

So it is hissing what do I do? Do you think that is the problem?

 

look for this check valve...if it's like the camaro.

https://www.thirdgen.org/forums/tech...-identify.html

one vacuum line goes to the a/c Duct Vacuum Control Valve, that's the little thing that control the a/c, heat, etc. In other words the top sliding lever.

Maybe one of those lines is leaking back there. That would be the vacuum leak James mentions.