1969 DeVille Thermal Vacuum Switch?
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500, 472, 425, 368 Discussion, 1969 DeVille Thermal Vacuum Switch? in Cadillac Engine Technical Discussion; I have what appears to be some kind of vacuum switch on my 1969 Deville. The ports are labeled D, ...
  1. #1
    Brother_B's Avatar
    Brother_B is offline Cadillac Owners Fanatic
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    Question 1969 DeVille Thermal Vacuum Switch?

    I have what appears to be some kind of vacuum switch on my 1969 Deville. The ports are labeled D, C, M, and F1. What is the F1? I am guessing that D goes to vacuum advance for the distributor, C goes to ported vacuum at the carburetor, and M goes to manifold vacuum. Is that right? Also, I think this may be the wrong vacuum switch for my car. My vacuum diagram only has a D, C and MT. Last, where should this thing be mounted once I figure it out? It doesn't have any threads on it to attach it to the intake manifold or wherever it is supposed to go. Maybe that parts broken off. The way I found it, it's just laying there. (It has a button sticking out that can be pressed in.)

    Thanks,
    B

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    The Ape Man's Avatar
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    Re: 1969 DeVille Thermal Vacuum Switch?

    IIRC they had a switch that supplied manifold vacuum to the distributor when the engine temp started to rise above normal. Later ones had the switch which delayed vacuum advance untill 3rd gear or some other stupidity. I'd plumb the ported carbonator vacuum right to the distributor and call it a day. Those old bi-metal switches would really need to be tested for proper operation befopre considering use.

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    Brother_B's Avatar
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    Re: 1969 DeVille Thermal Vacuum Switch?

    Thanks. I was going to connect the ported vacuum straight to the distributor as part of my troubleshooting. If it seems OK, maybe I'll leave it like that. From what I can tell, you are right, the purpose of the switch is to change from ported vacuum to manifold vacuum at higher temperatures. Would that advance the timing to allow the engine to cool down some? Am I in danger of overheating if I run straight from the carb to the distributor? The way it's routed right now, one of the lines runs to the firewall. Is this line probably for the climate control switches?

    Thanks,
    B

    PS-Trying to post a pic...

  5. #4
    The Ape Man's Avatar
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    Re: 1969 DeVille Thermal Vacuum Switch?

    I think you have it correct. The line through the firewall probably supplies manifold vacuum to the HVAC and parking brake auto release. Yes, the idea is to advance the timing at idle in order to make the engine run cooler. I always removed the points distributors and went to later H.E.I. and it's full manifold vacuum distributor so have no info concerning overheating at extended idle. That switch pictured is of course quite useless unless it is physically connected to the engine block to sense temperature.

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    BluEyes's Avatar
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    Re: 1969 DeVille Thermal Vacuum Switch?

    It was the early ideas of what to do to reduce emissions - less timing. Yeah, uh, that was wrong though.

    Anyways, there was a switch that stopped the distributor recieving any vacuum untill the trans was in top gear as well as the thermal switch. You are right on that the extra timing (from the dist getting full manifold vac) helps cool the engine. It also raises the idle speed, so more airflow from the fan. Pretty slick really, but kinda silly at the same time.

    That vac switch should be attached to the front of the block, near the distributor. The button is probably the valve that would be pushed on by the thermostat portion which is likely still on the block or else replaced by a plug. If it is broken, probably best to junk it entirely since it won't do a thing flopping around like that.

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    JTraik is offline Cadillac Owners Enthusiast
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    Re: 1969 DeVille Thermal Vacuum Switch?

    I was able to purchase a new one of these through partsamerica.com, 30 bucks.

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    DrtyJack75 is offline Cadillac Owners Member
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    Re: 1969 DeVille Thermal Vacuum Switch?

    hey Brother B, I saw another post that you said you might be able to hook the guy up with a wiring diagram? Any chance I get a copy of that too??

    I just put a donor 425 (cause it was available, LOL) in a 69 were building and am having a heck of a time figuring out all those wires and vacuum lines under the hood.

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    caddydaddy69 is offline Cadillac Owners Member
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    Re: 1969 DeVille Thermal Vacuum Switch?

    --------------------------------------------------------------------------i am trying to post on any thread that deals with vacuum on a 1969 cadillac i am trying to find where on little hose goes this hose comes out of a grommet in the firewall and connects to the a/c control in the dash the grommet is round with what seems to be a screw at the top and bottom it is black with a green stripe and has a splice in it (apparently it broke at some time in the past) but where it goes nobody knows. go to 368, 472, 500 forum and click on vacuum then 69 70 vacuum wiring and look at that vacuum solenoid in the diagram does a 69 have this solenoid or just 1970? any help would be appreciated

  10. #9
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    Re: 1969 DeVille Thermal Vacuum Switch?

    Brother B, that three port switch is supposed to screw into the front of either the driver side head or the front of the engine near the distributor. It senses engine heat and uses a wax bulb to open up or close off the ports depending on how hot the block is. I'm not at home but the shop manual goes into this. I think mine has three ports not 4 (1968) but they might be the same, since the 1968 and 1968 engines had VERY FEW differences and most were not block related (cooling system was different for example).

    My 68 is still getting body work re-done.

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