# Thermo vacuum switch



## Nicholas (Jan 16, 2017)

Hi everyone. My '71 GTO came with factory a/c. When I first bought the car, some pieces were missing and since then, I've been buying parts to put it back together. A missing piece is the thermo vacuum switch that screws into the passenger side intake. I've researched this part and I see it is offered in a 5 port and 3 port variety. I do believe I would need the 5 port. Would that be correct?? I've also checked the schematics in my repair and assembly manuals, but can't seem to locate where this switch gets it's vacuum from. Would anyone know that?? Thank you very much.


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## Pinion head (Jan 3, 2015)

For '71 only 455 HO equipped cars used the thermostatic switch with rubber stob & 3 vac lines. D-port cars used the three prong thermostatic switch, which '71 HO cars also used on drivers side water crossover outlet when equipped with factory AC.


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## integrity6987 (May 10, 2017)

vacuum is essentially any pressure lower than atmospheric pressure. Like when you suck soda from a cup. The source of vacuum is as you stated - the intake manifold. under low engine load a vacuum is created by the open intake valves and downward travel of the pistons on the intake stroke.


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## tjs72goat (Jul 20, 2017)

Correct me if I'm wrong. But, the aforementioned switch is actually vacuum operated by the temperature of the water that opens the switch for vacuum. I believe it is mostly for emissions purposes and gets ported to the charcoal canister for one. Therefor, I have to ask if it's even necessary to install if one isn't using a charcoal canister?


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## Nicholas (Jan 16, 2017)

tjs72goat said:


> Correct me if I'm wrong. But, the aforementioned switch is actually vacuum operated by the temperature of the water that opens the switch for vacuum. I believe it is mostly for emissions purposes and gets ported to the charcoal canister for one. Therefor, I have to ask if it's even necessary to install if one isn't using a charcoal canister?


I'm trying to put my factory a/c back together, but I really don't know exactly what it looks like, because it came missing parts. Already, I have a deficit. I've looked in my repair/assembly manuals and can't find a good schematic of mainly electrical and vacuum that pertains to operating the a/c. Also looked on line and can't find anything definitive. I inquired about this thermos vacuum switch, because I thought it was part of the a/c. I just read where it's not. Has more to do with the charcoal filter, which I'm not using, the carb. and distributor. Basically emissions. Nothing mentioned about the a/c. So, that is my mistake. This is something that I won't be needing. I'm guessing that the a/c is basically electrical and the rest of the system, heat and defroster, allows the air via doors into the driver compartment, The doors are operated by vacuum from the dash switch. That's where my problem lies. Where the lines go, their origin, source, etc.?? I'd like to have something to look at, but don't know where to find it. Thank you for the responses.


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## Pinion head (Jan 3, 2015)

tjs72goat said:


> Correct me if I'm wrong. But, the aforementioned switch is actually vacuum operated by the temperature of the water that opens the switch for vacuum. I believe it is mostly for emissions purposes and gets ported to the charcoal canister for one. Therefor, I have to ask if it's even necessary to install if one isn't using a charcoal canister?


The thermostatic valve you are thinking of is the '72 PURGE valve. Own three '72's, all use that valve. '71's, like mentioned before, only use the 5 port thermostatically controlled Vac style switch on 455 HO cars. Though 5 ports on the switch, only 3 are used. The stob and three hose set-up feeds vacuum to the distributor. This thermostatic vac switch is the same as was used on most (but not all) '68 & 69 Pontiac intakes. 

The switch the OP is speaking of was used in both 1970 & 1971. Though they look the same, the '70 version has a different heat range than the 71 version. Either of these thermostatic electrical switches has three spade lugs that come out the top. There is a small jumper harness that plugs into the 3 prong switch & then plugs into the engine harness. On '71 D-port engines with factory AC this switch goes in the tapped hole in the passenger side of the water crossover. The drivers side hole is for the water temp switch, whether idiot light style or rally gauge style. On '71 455 HO cars with factory AC, the three prong switch mounts in the hole in the drivers side of the water crossover. The engine is out of my only '71 keeper with AC, will try & come up with a pic.


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## Nicholas (Jan 16, 2017)

A pic would be great. Thank you very much.


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## Nicholas (Jan 16, 2017)

*Heater control valve*

Another quick question. I've been looking at some diagrams and studying schematics in re. to vacuum and electrical involving a/c and heating. I'm starting to figure out some of this but I can't find where the vacuum line from the heater control valve goes to. I'm thinking it goes inside to the heater-a/c switch on the back of one of those ports, but I'm not sure. I know where it ends up alright, but don't know the origin. Would anyone know this?? Thank you.


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## tjs72goat (Jul 20, 2017)

Not to hijack this thread, but since PH brought it up. On a 72, does the temp sender go in the crossover too? I asked this somewhere before and someone said in the passenger side head. What is correct?


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## Pinion head (Jan 3, 2015)

tjs72goat said:


> Not to hijack this thread, but since PH brought it up. On a 72, does the temp sender go in the crossover too? I asked this somewhere before and someone said in the passenger side head. What is correct?


72 model and later Pontiac V8's took the temp sending unit into the side of the cylinder head. All stock '72 model intakes only has the hole for the Purge valve in the passenger side of the water crossover. The spot on the drivers side was not machined & tapped for a fitting of any kind.


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## Pinion head (Jan 3, 2015)

Nicholas said:


> A pic would be great. Thank you very much.


Nicholas, do you have a copy of the '71 Pontiac Service manual or the '71 LeMans/GTO/GP assembly manual? 

Can describe the path of this harness piece, it should be a part of your '71'a engine harness if car was originally equipped with AC.


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## Nicholas (Jan 16, 2017)

*pics of vacuum lines*

Would anyone have some closeup pics of their vacuum lines on a '71 GTO with factory a/c, they could post. I'm not using a thermo vacuum switch, so I wouldn't need to see those pics. I think I have most of the vacuum and electrical stuff figured out, but I'd like to confirm it by looking at some pics. I think 1970 might be similar. I've checked some manuals and other sources, but come up a little short. My interest is from the ports on the back of the heater switch, through the firewall and where they go from there. Thank you.


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