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Vacuum driven heater valve

elyon

elyon

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Should there be a vacuum driven heater valve on the supply side hose to the heater core in my truck? Many things had been removed by the PO. I currently have a ball valve installed to stop the flow in summer. If there should be one, where does the vacuum line come from at the firewall?

86 K20 Suburban
 
I think it would have to come from the heater control ,to open the valve when you put the temperature selector to "hot"...

Personally I'd just leave the ball valve in place--those oem vacuum heater valves were not that good,I have seen some rust thru and let coolant escape slowly until the engine overheated..they didn't always shut the hot water off to the heater core completely either..
 
I honestly don't know what the applications were that got them, but I've seen multiple statements that say some of the trucks got those valves.I just looked in the '85-88 parts manual and don't see one listed, but IMO the heater section of the parts manual seems to be lacking in clarity.

I've never seen one on a truck, I don't run one, but I can understand why you might want to. I also know that as mentioned, the OEM valves tended to fail...leak, stick in one position, you name it.

Not sure all the GM cars of the era got that valve or not, but I know it was more prevalent on them.
 
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They were used on most GM vehicles with A/C,so the heater core wouldn't have hot water flowing thru it year round, and "fighting" the A/C evaporator and lowering the efficiency of the A/C system..
I sold quite a few of those valves in the late 70's and early 80's..
 
Ahh. AC only would make sense. I never really dealt with AC on these trucks, so probably why I never noticed the valve. Even in summer without AC, I can see how cutting the flow off would help. Of course, so would floor insulation, etc. :)
 
I had to add shut off valves to my '72 K5...it would get hot enough on the bare floors up front to fry an egg on the trans tunnel,and after I installed a rear heater I got from an old school bus,I had to have the means to shut off both hoses going to it in the summer or I'd be roasted alive in it..

I used almost 40 feet of heater hose in do the install--at first I just plumbed the rear heater up "direct" with no shut offs--that proved un-wise one day when one of the rear heater hoses had a zip tie come off and let it lean against one of the mufflers...lost almost all the coolant!..:doah:..

I ended up arranging 4 valves so I could have the front heater only,the rear only,or both--or both shut off...that way if any of the heaters or hoses leaked I could just shut off the valves and fill the radiator back up,keep driving, and fix it later at my leisure..
One day while I was at a gas station checking my oil,the owner came out,looked under the hood,and said "you got a license to do all that plumbing" ?...:eek:..
 
They were only used on Suburbans with rear heat. When you used the rear heat it operated the valve to allow water to flow to the rear heater.
 
BUMP. I am trying to sort some of my dash stuff out. 83 K5 originally had AC. Got a small hard plastic hose coming out from the heater box area in the engine compartment, vacuum I assume, never been hooked to anything. When I suck on it I get continuous air. I'd like to know where it goes to and where it might be leaking. My heater works great and maybe I would put the AC back in later if it were easy enough.
 
It went to a tee above the distributor. One side to manifold ,with a one way valve, and other side to a vacuum
ball on driver side of engine compartment
 
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