Heater and Vent Work, But not Defrost? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

LBJ · 01-06-2008, 02:44 PM

I can get lots of heat in the cab, but not to the windshield. I don't depend on this truck in bad weather (or any time) so am not in a panic to get it fixed. But, like everything else on the truck, I'd like to get it in working order. Is it the selector switch on the panel? Missing vacuum hose? Stuck diffuser door?

LBJ

Ivan D. · 01-06-2008, 02:47 PM

A/C or not?

LBJ · 01-06-2008, 03:05 PM

Factory A/C.

swb85 · 01-06-2008, 03:29 PM

Mine does the same thing and so does my buddy's '85......and while I haven't had time to determine the cause/fix, I'll place my bet on this: Remove your glove box door and you'll see the top of the hvac "box". On top of that is a metal rod attached to a flapper door inside the "box". With your defrost running, actuate that rod with your hand and I'll bet your defrost starts to work. I haven't figured out why the door won't work on it's own (I think it's got to be a bad vacuum line/pod somewhere), maybe you can figure it out and tell me the answer so I can fix mine!

LBJ · 01-06-2008, 03:32 PM

SWB85,

That'll be easy to do. I still have the whole glove box out from putting the right door on. If I find the cause, I'll let you know.

Pyrotechnic · 01-06-2008, 03:58 PM

I have just the opposite issue. I get heat out of my defrost vents but not the main vents. Thats fine with me because I don't like the heat blowing directly on me and I've been plenty warm on my trips this winter, but I'd like to get it working anyway.

I'll mess with it and see what I can come up with.

knightlife · 01-06-2008, 08:57 PM

welcome to my world lol...

kevinr1970 · 01-06-2008, 10:20 PM

On my '82 K5 when I switch it over to defrost I get more through the AC vents (? the ones pointed towards you) then through the defroster vents.
I close those vents best I can and it helps but there is still a lot of "spillage" through the AC vents.

If I could get it locked into defrost I could live with that better than the way it is now?

killthewabbit · 01-07-2008, 05:40 AM

This is a valuable topic to me too. I can toast the rest of my cab, but not the windshield. I'm going to try the rod behind the glove box door also.

jokersbowtie · 01-07-2008, 07:45 AM

on my 84 it was a vacum hose under the hood

LBJ · 01-07-2008, 02:36 PM

Here's a page from a parts book I got at a swap meet. Shows the heater layout. Might be of help in figuring out the various problems with the heaters.

01-06-2008, 02:44 PM	#1
LBJ Registered User Join Date: Jun 2007 Location: TEXAS Posts: 378	Heater and Vent Work, But not Defrost? I can get lots of heat in the cab, but not to the windshield. I don't depend on this truck in bad weather (or any time) so am not in a panic to get it fixed. But, like everything else on the truck, I'd like to get it in working order. Is it the selector switch on the panel? Missing vacuum hose? Stuck diffuser door? LBJ

01-06-2008, 02:47 PM	#2
Ivan D. glamoros piece o' lowlife Join Date: Mar 2007 Location: Redford, MI Posts: 1,164	Re: Heater and Vent Work, But not Defrost? A/C or not? __________________ The more I drink, the more I drink, the more I drink... diesel, reg cab, long bed, 4 across the rear, single stack, wooden stakes, and lotsa lights - the Hay Express

01-06-2008, 03:05 PM	#3
LBJ Registered User Join Date: Jun 2007 Location: TEXAS Posts: 378	Re: Heater and Vent Work, But not Defrost? Factory A/C.

01-06-2008, 03:29 PM	#4
swb85 On a budget like Fred Sanford Join Date: Oct 2005 Location: Topeka, KS Posts: 2,031	Re: Heater and Vent Work, But not Defrost? Mine does the same thing and so does my buddy's '85......and while I haven't had time to determine the cause/fix, I'll place my bet on this: Remove your glove box door and you'll see the top of the hvac "box". On top of that is a metal rod attached to a flapper door inside the "box". With your defrost running, actuate that rod with your hand and I'll bet your defrost starts to work. I haven't figured out why the door won't work on it's own (I think it's got to be a bad vacuum line/pod somewhere), maybe you can figure it out and tell me the answer so I can fix mine! __________________ '85 Silverado swb: 383 stroker, 10.5:1, vortec heads, 232/238 roller cam, RPM air gap, performer 750 carb, stainless longtubes, 3" duals/super 44's, T56/4.11 383ci build / exterior refresh thread '98 Camaro z28: 370ci twin turbo 370ci build '01 Tahoe LT 4x4: 5.3, longtubes/ory, magnaflow duals, custom tune....wife's DD

01-06-2008, 03:32 PM	#5
LBJ Registered User Join Date: Jun 2007 Location: TEXAS Posts: 378	Re: Heater and Vent Work, But not Defrost? SWB85, That'll be easy to do. I still have the whole glove box out from putting the right door on. If I find the cause, I'll let you know.

01-06-2008, 03:58 PM	#6
Pyrotechnic Registered User Join Date: Feb 2007 Location: Austin, TX Posts: 3,930	Re: Heater and Vent Work, But not Defrost? I have just the opposite issue. I get heat out of my defrost vents but not the main vents. Thats fine with me because I don't like the heat blowing directly on me and I've been plenty warm on my trips this winter, but I'd like to get it working anyway. I'll mess with it and see what I can come up with.

01-06-2008, 08:57 PM	#7
knightlife Dark Heart Motorsports Join Date: Apr 2007 Location: 29404 DKFX Posts: 683	Re: Heater and Vent Work, But not Defrost? welcome to my world lol... __________________ How Deep Can YOU Bleed..? 1985 Chevy Blazer K5- 6.2 N/A, 400 turbo trans CUCV, 12v converted... a new chapter 2005 GMC Sierra Crew Cab 6.0 powwwaa!!! custom jumpseat install w/ captain seats, Hypertech tuner, MSD Blaster Coils, CB and twin antenna's, all electric interior, touch screen in dash. custom center console, with jump seat replacing original console. 1500 HD!

01-06-2008, 10:20 PM	#8
kevinr1970 Senior Member Join Date: Aug 2004 Location: Everett, WA Posts: 2,316	Re: Heater and Vent Work, But not Defrost? On my '82 K5 when I switch it over to defrost I get more through the AC vents (? the ones pointed towards you) then through the defroster vents. I close those vents best I can and it helps but there is still a lot of "spillage" through the AC vents. If I could get it locked into defrost I could live with that better than the way it is now? __________________ 2009 Honda Fit CfC (bsf 44.9 mpg) 2000 Tahoe Limited 1991 GMC CrewCab Dually 2wd, will end up swb, not dually and replace CCswb below 1991 GMC CrewCab Dually 4x4, just going to fix things up for now 1982/1989 K5/GMC Jimmy 2wd 1987 GMC 1/2 ton swb 2wd Crew (sold)

01-07-2008, 05:40 AM	#9
killthewabbit Spear and magic helmet! Join Date: Oct 2006 Location: Nashville, TN Posts: 1,226	Re: Heater and Vent Work, But not Defrost? This is a valuable topic to me too. I can toast the rest of my cab, but not the windshield. I'm going to try the rod behind the glove box door also.

01-07-2008, 07:45 AM	#10
jokersbowtie Registered User Join Date: Jul 2007 Location: Louisiana Posts: 74	Re: Heater and Vent Work, But not Defrost? on my 84 it was a vacum hose under the hood

01-07-2008, 02:36 PM	#11
LBJ Registered User Join Date: Jun 2007 Location: TEXAS Posts: 378	Re: Heater and Vent Work, But not Defrost? Here's a page from a parts book I got at a swap meet. Shows the heater layout. Might be of help in figuring out the various problems with the heaters.



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