Anyone Know What The Minimum & Maximum Vacuum Pressure is From a Slant6 ?

[Mopar Virgin]

We have placed an aftermarket AC system into my nonAC '68 Bcuda. It operates from a sliding mode selector (e.g. Off / MaxAC / AC / Defrost / Heat) that will not match to the original modes labelled on the dash bezel (e.g. Off / Defrost / Heat). I'm burdened with being very particular and am attempting to build it out using the OEM push-button configuration.

I've already gambled and bought a refurbished OEM push-button mode controller "With AC" ($350) that my engineering friend believes he can place 3 vacuum switches between it and the aftermarket AC system to enable the OEM operation/look (god help me). That, however, involves buying an expensive push-button versus slider mode configured dash bezel ($700) next, so we need to test all of this to validate.

So, I'm hoping someone out there knows the answer to the vacuum question titled on the posting so we have that datapoint in selecting the proper vacuum switch and configuring the system. And, whether there is a difference between model years I should be aware of?

 

[RustyRatRod]

Between 350 and 700 you could purchase an aftermarket control system such as Old Air or Vintage Air.

I can't make heads or tails out of your maximum minimum vacuum pressure question. What are you even talking about?

 

[mosleyme]

We have placed an aftermarket AC system into my nonAC '68 Bcuda. It operates from a sliding mode selector (e.g. Off / MaxAC / AC / Defrost / Heat) that will not match to the original modes labelled on the dash bezel (e.g. Off / Defrost / Heat). I'm burdened with being very particular and am attempting to build it out using the OEM push-button configuration.

I've already gambled and bought a refurbished OEM push-button mode controller "With AC" ($350) that my engineering friend believes he can place 3 vacuum switches between it and the aftermarket AC system to enable the OEM operation/look (god help me). That, however, involves buying an expensive push-button versus slider mode configured dash bezel ($700) next, so we need to test all of this to validate.

So, I'm hoping someone out there knows the answer to the vacuum question titled on the posting so we have that datapoint in selecting the proper vacuum switch and configuring the system. And, whether there is a difference between model years I should be aware of?

It will be 0 at full throttle. Maybe 20 at idle or when your foot is off the gas coasting. You can test and develop the system before buying the bezel.

Or dive into the deep end and design your own control panel.

Drawing and prototype shown. Want to do final in aluminum.

 

[Mopar Virgin]

Between 350 and 700 you could purchase an aftermarket control system such as Old Air or Vintage Air.

I can't make heads or tails out of your maximum minimum vacuum pressure question. What are you even talking about?

I do already have a Vintage Air system.

However ... Factory "WithAC" cars had a push-button controller for selecting the mode settings, which apparently operated off the engine's vacuum system, along with a slider below it for temperature setting. I am starting with a Factory "NonAC" car that uses a slide controller labelled with 3 nonAC mode settings (e.g. Off / Defrost / Heat).

Vintage Air asked that you use that to control the mode settings, but a "NonAC" sliding dash bezel does not have "MaxAC" or "AC" settings labeled.

We are attempting to engineer a means of removing the mode slide controller and inserting an original refurbish push-button controller into the equation. This requires some electronic parts (vacuum pressure switches) to convert the vacuum operated OEM refurbished push-button controller to send a proper signal to the Vintage Air system. That way I'm not stuck with a new 5 setting operation (e.g. Off / MaxAC / AC / Defrost / Heat) that is now labeled incorrectly with the old 3 nonAC settings (e.g. Off / Defrost / Heat).

The three "widgets" (e.g. vacuum controller switches) that we need to buy at ~$100ea have various vacuum pressure ranges they operate properly under, hence why I'm inquiring.

 

[slantsixdan]

I've already gambled and bought a refurbished OEM push-button mode controller "With AC" ($350)

What the eff‽ Y'mean an OE pushbutton selector like this, this, this, this, this?

I'm hoping someone out there knows the answer to the vacuum question titled on the posting so we have that datapoint in selecting the proper vacuum switch and configuring the system. And, whether there is a difference between model years I should be aware of?

There is nothing such as "maximum vacuum pressure". Pressure and vacuum are opposite; we say "pressure" to mean above atmospheric pressure, and "vacuum" to mean below atmospheric pressure. Also, the question doesn't make sense in context of what you are trying to accomplish. A running engine—Slant-6 or other—creates plenty of manifold vacuum at idle (around 20" at sea level) and cruise conditions, less vacuum under acceleration, and zero vacuum at WFO (wide-open throttle). A vacuum reservoir with check valve—like this, this, this, this is used to store vacuum so the HVAC modes can still be shifted even with the accelerator on the floor on the way up a mountain.

The mode selector doesn't send out a specific or calibrated amount of vacuum to active ports, it will either connect them to vacuum or not, depending on which button is pushed.

 

[RustyRatRod]

Ok. That helps. So you're talking about engine vacuum. Max at idle or cruise will be somewhere from 17-22" HG. There is no pressure involved.

 

[ProjectBazza]

The mode selector doesn't send out a specific or calibrated amount of vacuum to active ports, it will either connect them to vacuum or not, depending on which button is pushed.

 

[MadScientistMat]

It will be 0 at full throttle. Maybe 20 at idle or when your foot is off the gas coasting. You can test and develop the system before buying the bezel.

Unless you've really gone crazy with your build and have negative vacuum at full throttle. For forced induction, or even an engine with a big cam, anything vacuum operated needs a reservoir and check valve. Some Lotuses used an infamous vacuum operated pop up headlight design that would retract at full throttle.

 

[Mopar Virgin]

What the eff‽ Y'mean an OE pushbutton selector like this, this, this, this, this?


There is nothing such as "maximum vacuum pressure". Pressure and vacuum are opposite; we say "pressure" to mean above atmospheric pressure, and "vacuum" to mean below atmospheric pressure. Also, the question doesn't make sense in context of what you are trying to accomplish. A running engine—Slant-6 or other—creates plenty of manifold vacuum at idle (around 20" at sea level) and cruise conditions, less vacuum under acceleration, and zero vacuum at WFO (wide-open throttle). A vacuum reservoir with check valve—like this, this, this, this is used to store vacuum so the HVAC modes can still be shifted even with the accelerator on the floor on the way up a mountain.

The mode selector doesn't send out a specific or calibrated amount of vacuum to active ports, it will either connect them to vacuum or not, depending on which button is pushed.

I got a total kick out of your reply "schoolin' me" about misuse of pressure (e.g. negative pressure) vs vacuum. It is exactly what my engineering friend helping with this would say as well to me as well ... along with a diatribe about the intricate details surrounding it that would lose me in the first sentence. As a mere mortal outside the engineering world, the concept of negative pressure seems logical, but hey, what do I know?!!!

Thanks for the info you provided. I got it in my friend's hands last night to assess against the design he has us pursuing to make sure we understand all the factors and don't go down a rabbit hole with my wallet. I might be coming back to you if we get jam figuring this thing out ... thanks again !