Vacuum for heater shutoff

[Novasmihjohn]

Does anyone know where the vacuum originates for the control valve for the heater water shutoff valve? I found the line and it went to the drivers side of the engine but couldn’t locate where it was connecte.

 

[SUBURBAN5]

Take a pic of your set up, vehicle are slightly different. Suburban vs tahoe vs c/ k 1500 pick up

 

[GoToGuy]

Pickups don't use it. Only Tahoe , Yukon, subs.

 

[GoToGuy]

Always start with Year, Make, Model, eng, trans. You tell the parts counter what you have right? It can make a big difference on the correct answer. Some won't bother to answer. They look the same twenty feet away,but open doors and hood there all different. If you had the factory OE service manuals you could have already had the answer. Not knowing what year is it this?

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[1998_K1500_Sub]

Pickups don't use it. Only Tahoe , Yukon, subs.

I won't claim you're wrong or that I'm right, but...

I was of the impression the 4-door truck cabs got it too. I seem to believe I saw that referenced in an FSM somewhere.

(edit) Well, I think I was mistaken. At least in my 1998 FSM, all they mention is the 4-door utility vehicles (Tahoe / Suburban / etc.) with gasoline engines; see last sentence here:

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and

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FWIW, I once noticed my Suburban's solenoid-actuated vacuum valve was plugged and wouldn't move air, so I used some Brakleen to blow it clear.

I'm not sure if the vacuum valves are available anymore as service items. The last time I was in the treasure yard I snagged three of them to keep as spares.

I've seen replacement solenoid-actuated vacuum valves for Toyotas that might serve as service items for the GMT400.

 

[evilunclegrimace]

I won't claim you're wrong or that I'm right, but...

I was of the impression the 4-door truck cabs got it too. I seem to believe I saw that referenced in an FSM somewhere.

Do 4 door truck cabs have a rear heater??

 

[1998_K1500_Sub]

Do 4 door truck cabs have a rear heater??

Sorry, I updated my original post with more info.

Evidently the 4-door utility vehicles (Tahoe / Suburban) are the ones that got it.

Regardless, the valve shunts the coolant flow to the front heater core and, in a larger-interior vehicle (like a 4-door crew cab) I could see the value of having one, regardless of whether GM provided one as OE.

 

[GoToGuy]

This is one of the diagrams, and I read the operation paragraphs. In one area states " Gasoline Utility, Suburban only". In the second diagram , " Gasoline Four Door Utility, Suburban " . So the Tahoe and Yukon are GM's Utility model and are available in two and four door. It makes perfect sense when selecting max cold at detent it shuts off heater water for maximum cooling air for large interior space. Since it doesn't reference pickups , and I haven't seen one , I go with what's printed. If I come across a crew gasoline I will definitely check to see if it has a water valve. And amend the " note ".

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[1998_K1500_Sub]

This is one of the diagrams, and I read the operation paragraphs. In one area states " Gasoline Utility, Suburban only". In the second diagram , " Gasoline Four Door Utility, Suburban " . So the Tahoe and Yukon are GM's Utility model and are available in two and four door.

I think you and I are on the same page now. I was mistaken earlier w/ my comment about the 4-door cab models, although I still see value in having the water valve in the 4-door cab... when carrying 7 landscapers in the cab the AC needs all the help it can get.

For the record, to clarify for the readers, the FSMs indicate it is the 4-door utilities, i.e., not the 2-door Blazer / Yukon utilities, with the gasoline engine that got the water valve / solenoid operated vacuum valve.

 

[east302]

My two-door Tahoe does have that valve and I think I measured a degree or two a/c temperature difference a few years ago when I tested it. It’s better than nothing, I suppose, but rear air and a higher flow blower would have been really nice instead.

It sounds like GM couldn’t quite make up its mind when they did the manual.