1980 C10/C15 Heat Risers, closed or open??

[shpark]

My heat riser is always open, I have the rod style to the EFE vacuum pulloff mounted on passenger exh. manifold. This makes sense to me, if system ever failed - spring inside the pulloff would force the valve to fail open and not restrict exhaust. Whatever is installed where my EFE TVS is supposed to be, is not working. It is blocked when it's cold and when it's hot, personally I think it might be a oil pressure activated vacuum switch instead. I want to find right part before full on winter hits, the quick warmup would be ultra nice.

Problem #1: I have had people tell me this is backwards. Parts guy I saw today who used to own 79 Blazer, says his would rattle until is was full open and under tension from EFE vacuum actuator, and full vacuum from EFE ported vacuum switch. I was under truck tonight to check, mine is open when cold, I tried to flip it around so to make it work in reverse - it can't be done.

Problem #2: It seems that most ported vacuum switches I have found for sale (not many mind you) are normally closed, this does not help me get vacuum to close my heat riser after startup. I need a two port normally open vac switch. My vacuum advance vac. switch (SPARK TVS) is normally closed, it's mounted on the water neck.

SO, I need to know - of those of you who still have vacuum operated heat riser's (no laughs please). Do they get pulled shut immediately after startup, and then slowly open as vacuum is cut off? Or are they already closed, and slowly open as vacuum is introduced?

If someone has been through this before I would love to hear from you. I think another problem is the 500 bazillion vacuum diagrams for 1980, I swear Autozone has 30 posted on their website - that surely won't include any Canadian funny business either - I found one that is darn close to mine regardless. I can post it and pics of my 5.7L vac hose disaster if need be.

[PhilaTruck]

There was someone recently, guy has a van I think. I'll try to remember who. In the meantime, you might want to search in the engine & drivetrain forum.

[shpark]

Got this sorted, went to the wrecker and pulled vac switches of a caprice, cadillac, GM van, pontiac parisienne and a chevy truck. And I found my tiny vac check valve off another old van. 5 bucks for it all. Hooked er up last night, works great!