Something's wrong with the defrost.

[ootdega]

So, this is my first car, so I don't have any pre-existing standard by which to judge how some things are working. One of these things is the climate control. I thought it was working properly, but upon further investigation, I am an idiot.

The problem is when I set the switch to defrost, it mostly blows air through the front vents and only kinda-sorta onto the windshield. The rear defrost works better, which should have told me it wasn't working right in the first place, but whatever. Hindsight is 20/20 and whatnot.

There are a few other odd things it does that might be related. When I turn on the power, there's a plastic-sounding squeak behind the glovebox. When I then start the car, there's a much louder and longer squeak which seems to sound like something opening. When I turn the car off, it makes a series of squeaks that clearly sounds like something large and plastic closing.

This has to be what's causing it, but I have absolutely no idea what is even behind the glovebox, let alone what there could be making such WEIRD noises.

Whatever it is, I get the impression it's going to be expensive to fix. What can you guys tell me?

[GM_Guy]

As you change positions, does air come out of anywhere else (More going to your feet when you have floor selected, more going to the other positions as they are selected)? If not, you may have a vacuum issue to address.

The HVAC system opens and closes the vent door depending on where your control is sitting. One of them slams shut a couple seconds after the car is shut off.

The squeek may be the blower motor/cage rubbing if by power on you mean turn on the hvac.

It can be expensive if you need to pay somebody else to do it. If you need somebody else to do it, best to seek out someone who has actually done a few of these specific cars. If no one else has, you may as well be the one to use it as a learning experience rather than them becuase they will fuck it up, and it will cost you more money.

Alex.

[ootdega]

By "connecting the power" I mean turning the key without starting it.

It sounds like a vacuum problem, based on what you said. If it's supposed to slam shut, and it's just slowly squeaking closed, then it's because something is weak.

Now that I think about it, the floor setting doesn't work either. So basically it only blows air through the front. It -wants- to do what I tell it to, it does get -some- air to the windshield, but something isn't opening far enough for it to do so efficiently.

I'll ask the shop I normally go to if they can do it, because I'm going to have to get it done if I don't want to freeze my ass off again.

[gadget73]

sounds like air plenum door hinge failure. Mine had this exact problem. The fix is taking the whole dashboard apart to extract the air plenum, then rebuilding it with small metal hinges to replace the broken plastic parts. Its a pain in the ass. Replace the heater core if you're in that far. It basically has to come out anyway to get the plenum out.

[pantera77]

sounds like air plenum door hinge failure. Mine had this exact problem. The fix is taking the whole dashboard apart to extract the air plenum, then rebuilding it with small metal hinges to replace the broken plastic parts. Its a pain in the ass. Replace the heater core if you're in that far. It basically has to come out anyway to get the plenum out.

Yep, common problem. Hinge is broke in the winter wagon, and I've been to lazy to fix it. I just close all the vents which force some air out the defrost.
I did a few on 05+'s, same exact door (and air plenum) as boxes have.

[GM_Guy]

Exact same plenum? I guess that begs the question, will a 1990/91 plenum fit in an 88/early 89? (heater core size changed late '89). Opens the door to a few more possible swaps if the 05+ plenum can be installed in a box.

Alex.

[ootdega]

sounds like air plenum door hinge failure. Mine had this exact problem. The fix is taking the whole dashboard apart to extract the air plenum, then rebuilding it with small metal hinges to replace the broken plastic parts. Its a pain in the ass. Replace the heater core if you're in that far. It basically has to come out anyway to get the plenum out.

Sounds good. Any preferred make? The Motorcraft is twice as much as anything else on PartsGeek.

Exact same plenum? I guess that begs the question, will a 1990/91 plenum fit in an 88/early 89? (heater core size changed late '89). Opens the door to a few more possible swaps if the 05+ plenum can be installed in a box.

Alex.

That's a good question. Can that be done? I might as well if it can.

[gadget73]

The first core I put in my car was a Motorcraft and it leaked out of the box. Didn't think to pressure test it first, so I drove around for 2 years with a leaky heater core until I couldn't stand it anymore. The replacement was fine, but I did pressure test it before installing it. Not sure what else is good/bad. I'm half convinced it all sucks some days. Also, try Rockauto. They probably have a discount code posted on here in the vendor forum.

[ootdega]

The first core I put in my car was a Motorcraft and it leaked out of the box. Didn't think to pressure test it first, so I drove around for 2 years with a leaky heater core until I couldn't stand it anymore. The replacement was fine, but I did pressure test it before installing it. Not sure what else is good/bad. I'm half convinced it all sucks some days. Also, try Rockauto. They probably have a discount code posted on here in the vendor forum.

Yup, found it. Thanks.

I've been reading good things about the Spectra Premium cores, but I'll do more research before making a decision.