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Where to start with heater control problems?

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Big6ft6

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I did a little searching and found a lot of answers to specific questions, but could anyone give me a general "where to start" with non-working heater controls? Or general description of how they work?

I have heat in the winter and when I slide the control to cool, it brings in cool air (I think). But none of the position controls work, i.e. defreost, etc. No matter which setting I have it on, heat only comes from dash vents.

I really need defrost in the winter. I have an A/C (deleted by me) 89 burb. so it is vacuum controls right? This is a big driveability issue.

Thanks in advance!
 
I would guess that it's:

1. No vacuum to the controls. Check the vacuum lines and connections from the engine. Are they cracked/split? Disconnected? Non existent? Routed wrong? Also check any rubber couplers, they can wear out.

2. The actuators are worn out. Use a vacuum tester connected to each one to determine if this is the issue.

3. The control switches are "dry". I think they have to have a little grease in them to keep them sealed. Take it out of the dash, inspect it, determine what kind of grease (if any) should be in there.

4.Vacuum leaks in the engine. Be sure you don't have a loss of vacuum somewhere else, as low vacuum may be the cause.

5. Zombies.
 
Thanks Jessie,

Where does the vacuum line go through the firewall from the engine bay?
 
When you move the control, do you hear any sort of "vacuum" noises?

You can normally hear it switching modes if there is vac to it.
 
The vacuum line(s) go through on the passenger side. As I recall, they come off the block near the intake, go towards the center of the firewall, then along to the right side and into the firewall. I believe there is a check valve in the line too.
 
Man, it's been a long time, but I overhauled the vac system on my 84 many moons ago. Let me see if I can dredge up the thread for you..........

******EDIT******

It looks like the thread I was looking for is no longer in the archives. Anyhow, I'm willing to bet your problem can be traced to a broken plastic clip that controls the vacuum-actuated diverter door under the glove box. For more info, search the term "defrost" by username "Can Can". There should be enough tidbits in those threads to help you start diagnosing your issues. Keep us in the loop, brother.
 
Thanks to this thread I just fixed mine. The heater would blow but nothing from the dash vents or the defroster. I started tracing the hose from the vacuum reservoir at the drivers side firewall ans found that it was hanging loose behind the intake manifold. A little searching turned up a tee with another broken hose hanging from it. Connected the two and now I have heater controls. Thanks guys.

Sean
 
Dang, I've got to get out there and play with it I can't remember if there is vacuum noise. I know what you mean thought from other GM cars of the same vintage. Sounds like best bet is to just start chasing vacuum lines.

When I repalced the engine I pulled a bunch of vacuum lines in the area of the cruise control...jumped in the car and saw no problems, assumed they were just for the cruise. But it was summer then...and I can't remember if it had defrost when I first got it or not:dunno: I'll have to check.

Thanks for the ideas for searching "defrost"...duh..I was searching heater controls.
 
No problem, my friend. FWIW, if my reply helped you out, feel free to become a supporting member of CK5. Where else could you get that kind of online advice for $25/year????
 
So I've been tinkering with my vacuum hoses in hopes of restoring some of the features in my truck (like defrost)

I've found a large black plastic ball on the firewall, a bit bigger than a softball, way over in the driver's corner, that looks to have a broken piece of vacuum line on top of it. Is this a vacuum "canister"? Does the heating switch gear run off of that?

I also noticed a vacuum T coming off the manifold behind the throttle body, it has one vacuum line going to the brake booster, and a second nipple that I currently have capped, is this where the previously mentioned "black ball" was hooked to?
 
That black ball, as memory serves me, is either a vacuum reservoir so that you have vacuum in reserve or an emissions charcoal canister. I believe it should be kept hooked up.

It sounds like the second vacuum line you have capped off was the one that went to your heater controls.

Do you still have the vacuum routing sticker on your truck, near the radiator? That may help.
 
Your control vacuum goes thru the firewall just to the side of the A/C -heater box. It is a hard plastic line. It tees into the vacuum line going from the manifold vacuum to the "black ball". The ball is a reservoir so your controls work when accelerating and vacuum drops.
 
Ok, I just went and looked at my truck (1991). My vacuum ball has a line that goes to the middle, and behind the distributor somewhere. Another line (maybe the same one) comes up from back there, has a T in in, and on the small side of the T is a smaller hard plastic black line which goes over to where the antenna line goes through the firewall, and passes through the firewall.
 
On my 91 that black softball connected to a line behind the TBI with 2 tees. i would say the one you have capped should connect to the soft ball. I think it is a vacuum resevoir. Once i hooked that up my heater controls all worked.
 
Thanks Guys! I'm starting to get the picture. I was just out looking at my truck and I'm missing some parts. Nothing is hooked up, the black ball is not hooked up, nor is there a "T" at the back of my manifold, and I need to go look to see if there is any vacuum line going through by my A/C heater control/Antenna
 
So I just went and looked and I do not have any vacuum lines going throught the firewall near the heater core or A/C box. I don't even have a broken one hanging there??

Can anyone see where it goes after it goes through the firewall? I was peaking behind my glove box and couldn't see any vacuum lines or connectors, just a actuator arm for some part fo the vent system.
 
I can't believe that nobody has mentioned the little plastic piece that connects the blend door linkage to the blend door. It is a very common part that breaks and is still available at the dealer.
 
I don't have any vacuum noises when I move the control levers so I don't think I have any vacuum to the controls. I'm still trying to understand where the vacuum source connects to the heater controls. I will pull the controls out from the dash of the truck to see if I can learn more.

Looking under the dash now I can see a bundle of vacuum hoses with different colored stripes. I just can't trace them without taking the dash apart.
 
Can Can said:
Man, it's been a long time, but I overhauled the vac system on my 84 many moons ago. Let me see if I can dredge up the thread for you..........

******EDIT******

It looks like the thread I was looking for is no longer in the archives. Anyhow, I'm willing to bet your problem can be traced to a broken plastic clip that controls the vacuum-actuated diverter door under the glove box. For more info, search the term "defrost" by username "Can Can". There should be enough tidbits in those threads to help you start diagnosing your issues. Keep us in the loop, brother.
Click to expand...

AKbigsub said:
I can't believe that nobody has mentioned the little plastic piece that connects the blend door linkage to the blend door. It is a very common part that breaks and is still available at the dealer.
Click to expand...


:D :whistle:
 
So is the "blend door" what sends air to the defrost? I'm getting confused on what is vacuum-controlled and what is linkage-controlled, or does the vacuum move the linkage?

I don't appear to have any vacuum, but from looking behind the glove box the linkage appears to be intact.

Does anybody know of a vacuum hose digram for these trucks for the heater stuff? I can find 'em for the engine vacuum hoses, but not for once you get past the firewall.
 
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