Okay guys, have done a little reading but still not grasping how vacuum is generated and works.

I know many car systems are vacuum powered or activated, and understand the essence of what it is. But what on a car generates it?

The specific application I need it for is the HVAC system, it seems both the vents and the hot air to cold air use it to operate. The car does not have any vacuum hooked up right now. What do I need? I have seen references to vacuum motors but there is nothing in the shop manual or auto parts site that references it.

Any links that can educate me? Tried searching but this sites search engine eludes me, I get tons of off topic results....

Thanks, sorry for the newb question.

 

Locate the hard plastic line on the firewall that supplies vac to the HVAC control gear under the dash and hook it up to a engine vac port
You need a one way valve as shown to keep the vac constant otherwise your vent position will change everytime you accel .You should also have a vac canister somewhere that stores vac; that needs to be connected also

 

The piston goes down , it sucks air in (vac)
The same vac generated by the piston is what is used to operate the vac items ;taken off from the intake manifold which is under vac in most cond ; except WOT

 

Vaccuum is generated by the pistons moving downward on the intake stroke, pulling the air/gas mixture through the intake manifold. When the throttle plates are closed there is only a very small amount of air able to get past the plates and down through the carb venturies,much less than the volume of the cylinders displace and therefore a vaccuum (negative pressure as compared to ambient atmospheric pressure) is created.

I believe that when the throttle blades are opened, vaccuum will drop because the obstruction of the air movement gets taken away, until the increase in RPM's makes more vaccuum and comes closer to having the venturies (with open throttle blades) become a restriction in the flow of air, therefore a bit of vaccuum will be present again.

If you have a turbo or supercharger in a blow- through carburetor system, you will get positive pressure through the venturies as long as the compressors are turning and hooked up to the intake tract.

You can get a strong vaccuum source from a hose fitting nipple plumbed into the venturi section of the carb below the throttle plate, and a milder source of vaccuum from a fitting running into the venturies above the throttle plates. Carbs will have both types of ports, and you can pull below- the throttle- plate vaccuum off of the intake manifold plenum or runner area.

As has been said previously, a check valve will eliminate pulsing and vaccuum drops (spikes?) and a cannister ball will hold and store vaccuum and can act as a vaccuum distribution manifold.

 

Thanks everyone for their input. I will do some searching for vacuum ports when I get in there Friday night. Does the hot air to cold air operate off vacuum also? Does anyone have a diagram for where the vacuum goes on the climate controls? I have the shop manual, and would have expected a diagram, but sure can't figure out where it is if it is there.

Thanks again.

 

all you have to do, is supply vacuum to the plastic hose going into the passenger compartment, behind the engine there, as in the pic above. The HVAC controls will take care of it from there.

 

The vacuum line your looking for is hard plastic, and enters the firewall just to the right of the heater box, through the same hole as the wires for the blower motor. You'll want a vacuum line coming off the port at the back of the intake, to run to a check valve, the line then splits off the check valve to the vacuum line at the heater box, and also around the driver fenderwell to the vacuum ball that is under the driver headlight.

You also need vacuum to the power brake booster - should be a much larger line running from the back of the carb, to another check valve, and into the brake booster.

Should also have a vacuum line to your distributor (assuming you have an aftermarket HEI with the vacuum can on the side - this usually comes off the front of the carb.

Also have a vacuum line running to a PCV valve in one of the two valve covers, usually a larger line like the brake line, only comes off the front of the carb as well.

That's the major required lines, assuming you're a carbed engine.

If there's EGR, it gets a line as well. So does any MAP sensor. Also, the evap canister if you have one, and cruise control.

 

Thanks for all the input guys, hopefully I can knock this out tomorrow night along with my cooling system rehash.

 

Ok about this vacuum ball.... i have a 92 rs 3.1 and i remember pulling a large vacuum line off that ran down the driver fender. It wasnt connected to anything and i dont remember seeing a ball. Would this be something that fell off?? let me know please

 

Okay went to the junkyard and looked at my own engine and I have some more insight now. There are 4 colored vacuum lines going into back of HVAC controls, previous owner cut them but still routed into behind console. Did not trace them into engine bay. Does anyone have a diagram of where each of these lines is going?

Thanks.

 

They go to the vac pots on the HVAC .Need shop manual

 

They don't run through to the engine bay - just under the dash to the locations where they change vent routing.

 

ok i figured out my heat problem. it wasnt the vacumm after all. My cooling system wasnt cycling back to the water pump. There might be a plug in the new water pump i installed. I didnt check for it but my uncle said sometimes they put plugs in them due to most people have the return line go to the radiator which is what we did to get the heat working.