No Defroster

[crawdad]

I hope some of you guys can tell me what to check or look for. I'm not getting any air at all through the defroster . I've taken the glove box out and some of the air ducts to see if a vacuum line might be off, but I couldn't find anything. Everything looks ok, but admittedly it's a bear trying to find something underneath that dash. I know some of you folks have gone through this before, but I couldn't find anything by doing a search. Any help would be very much appreciated.

[eagle23]

Is it coming out just through the heater vents?

Reason I ask is my '77 does that, and a really good AC guy said it was the little vacuum valve that controls the doors directing the air. He said it was behind the glove box, and maybe a bit deeper than that. I haven't replaced it yet, so I apologize for the vagueness. It's not that expensive a part, and he wanted $300 to do it, mostly labor. He said it wasn't hard, just a PITA.

I'm sure others can enlighten more here.

[mySAVIOReigns]

I know this really doesn't answer your question, but I know of a MUCH better defroster. If you open the vent windows and drive, they are GREAT at defrosting the window - much better than the defroster.

Anyways, to the question at hand, just like eagle said, there is a "switch" that throws it into the right position when you move the toggle bar. I would start at the unit, and head down it until you find something. Could be disconnected somehow...

[Jonboy]

the vacuum switch is on the A/C control head on the dash.

[mhicks]

What year are you talking about?

[crawdad]

Originally Posted by mhicks

What year are you talking about?

It's the '86 Silverado in my signature line.

[crawdad]

Originally Posted by Jonboy

the vacuum switch is on the A/C control head on the dash.

I'm not getting any vacuum coming off of this switch. Can you tell me where the scource comes from?

[crawdad]

Not sure if this is the correct name for this, but I'm calling it the vacuum pod. It is the round plastic pod mounted to the firewall, next to the power brake booster on my 86. My question is, does this pod pull a vacuum? I disconnected the vacuum line coming from it and am not getting any sort of vacuum either coming from it or going to it? Exactly what is its purpose and what would happen if one were bad. I'm still trying to chase down why I'm not getting any defroster. Thanks.

[84 400]

i don't have that pod and mine works fine. I am not really sure why yours is not working unless it is the valve explained before. does it have heat? IF the hea and blower are working fine it must be the door valve as stated before

[crawdad]

It might be the switch valve, but I don't think I'm getting any vacuum to it at all. There has got to be vaccum supplied to it in order for it to work correctly, right? Evidently my vacuum lines are all screwed up somewhere and I'm not getting any vacuum under the dash. That's when I started playing around with the vacuum pod. Not getting any to it either, but I don't have a clue what its there for or if it would have anything to do with my problem. Oh well, if anyone can think of anything for me to check, please do.

[Jonboy]

there should be a vacuum hose that goes right to the intake, IIRC. I think it goes through the firewall in a grommet right by the a/c box underhood.

[crawdad]

Originally Posted by Jonboy

there should be a vacuum hose that goes right to the intake, IIRC. I think it goes through the firewall in a grommet right by the a/c box underhood.

Yes, I found that hose, but it doesn't go directly to the intake. Instead, it runs along the firewall, behind the distributor and connects to a multi-connector over by the brake power booster. I didn't pull that particular line off to see if it was getting vacuum. I did pull another one off of that same connector and there wasn't any vaccum at all. If it wasn't on that one, then I don't guess it wouldn't have been on the one you're talking about either. Hmm, maybe that's the problem. You say it should run to the intake? Where exactly should it connect? Thanks.

[Bender]

My truck is no way near stock, but I’m sure I’m pulling the vacuum off the carb somewhere.

Years ago when I rebuilt my truck, I used a mityvac [sp?] hand held vacuum pump to pull a vacuum to check the system operation as well as check for vacuum leaks.

I actually found the vacuum switch by the controls to be leaking.

I ripped it apart and tried to put some vacuum grease in there but it still leaked and I replaced it with a new one.

So I guess what I’m trying to tell you is to get a vacuum pump and pull a vacuum on the system and check to see if it’s holding a vacuum. Under vacuum, you should be able to use the control lever to operate all of the heating vents. Check to see if it holds vacuum under all of the different settings.

I would really suggest for all of the people out there with vacuum assisted heating controls to do this because I know the valve goes bad after time, and it’s an easy way to check for any leaking vacuum hoses.

Hope this helps!

[crawdad]

Originally Posted by Bender

I would really suggest for all of the people out there with vacuum assisted heating controls to do this because I know the valve goes bad after time, and it’s an easy way to check for any leaking vacuum hoses.

Hope this helps!

Thanks, That sounds like the best way to check it for sure. Been wanting to get me one for a while now, so I'm going to get one tomorrow.