Air Box Vaccum Line Topic is solved

[MoVolvos]

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Pretty sure there is suppose to be a vacuum line there. The question is where does it go? That's a wiper blade attachment piece don't pay attention to it .

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Intake Flap.jpg (503.73 KiB) Viewed 1508 times

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[scot850]

If I recall that should have a pipe that runs up to the side of the airbox and helps control the position of the flap using vacuum.

Neil.

[abscate]

Engine vacuum tree up to double nipple on air cleaner valve , the other nipple goes back down to that nipple on the vacuum driven motor for the air door

The stock configuration is hard white nylon lines with small rubber elbows but many of those are replaced with vacuum line at this point in life.

Function. Vacuum to the air door is metered by the temperature inside the air box via the air box thermostat. The air door opens to allow cold air from the front port and closes to pull hot air from the elephant metal hose on the manifold

It is variable so that it tries to maintain a set point inside the air filter box

Pull that black thing out if the motor flap so that it can function

[MrAl]

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Pretty sure there is suppose to be a vacuum line there. The question is where does it go? That's a wiper blade attachment piece don't pay attention to it .

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Intake Flap.jpg

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Hi,

On my car, the 1998 v70 non turbo, that contraption that pipe is connected to is the vacuum actuator that opens and closes that flap you see in the big opening that is blocked up. That little pipe connects to the other side of the air box at another little pipe through a vacuum line. That other little pipe on the other side seems to be the thermostat. The thermostat senses temperature inside the air box and opens and closes according to temperature so the flap can open and close. The other side of the air box also has another little pipe on the thermostat that connects to the main vacuum line i believe.
The way it seems to work is the vacuum is always present but is only allowed to reach that vacuum actuator when the thermostat allows it which adjusts the flap (you have blocked up in the picture) to regulate the air temperature inside the air box.
As the flap opens or closes or is part way closed, it allows some fresh air in from the front port or takes in air from the manifold heater part in the back of the engine. The combination of fresh air and heated are is what ends up getting into the air box and so the air box temperature is a mix of fresh and heated air.
That seems to be the way it works on my car. I never got to test the regulation temperature yet though. That can probably be done if you have a spare thermostat. You can run an air line from an aquarium pump to the thermostat and heat the thermostat until it lets air through it. I got an air pump but that was after i reinstalled the air box so i didnt get to test it yet and i dont have a spare thermostat.

Here's a rough schematic...

MainVacuumLine----->-----Thermostat----->-----VacuumActuator----->-----Flap

[454cid]

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Pretty sure there is suppose to be a vacuum line there. The question is where does it go? That's a wiper blade attachment piece don't pay attention to it .

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Intake Flap.jpg

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Hi,

On my car, the 1998 v70 non turbo, that contraption that pipe is connected to is the vacuum actuator that opens and closes that flap you see in the big opening that is blocked up. That little pipe connects to the other side of the air box at another little pipe through a vacuum line. That other little pipe on the other side seems to be the thermostat. The thermostat senses temperature inside the air box and opens and closes according to temperature so the flap can open and close. The other side of the air box also has another little pipe on the thermostat that connects to the main vacuum line i believe.
The way it seems to work is the vacuum is always present but is only allowed to reach that vacuum actuator when the thermostat allows it which adjusts the flap (you have blocked up in the picture) to regulate the air temperature inside the air box.
As the flap opens or closes or is part way closed, it allows some fresh air in from the front port or takes in air from the manifold heater part in the back of the engine. The combination of fresh air and heated are is what ends up getting into the air box and so the air box temperature is a mix of fresh and heated air.
That seems to be the way it works on my car. I never got to test the regulation temperature yet though. That can probably be done if you have a spare thermostat. You can run an air line from an aquarium pump to the thermostat and heat the thermostat until it lets air through it. I got an air pump but that was after i reinstalled the air box so i didnt get to test it yet and i dont have a spare thermostat.

Here's a rough schematic...

MainVacuumLine----->-----Thermostat----->-----VacuumActuator----->-----Flap

That's a good explanation of how it works. I don't think your method of testing will work, Though. The pump produces pressure, not vacuum. You would need something like a hand held Mighty Vac vacuum pump for testing.

I did temporarily use aquarium air line for one of the connections on my 850.

[MoVolvos]

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Thanks everyone! I will take a look at it in a few days when I reinstalled the ABS Module, weather permitting. Raining today.

.

[MrAl]

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Pretty sure there is suppose to be a vacuum line there. The question is where does it go? That's a wiper blade attachment piece don't pay attention to it .

*
Intake Flap.jpg

*

Hi,

On my car, the 1998 v70 non turbo, that contraption that pipe is connected to is the vacuum actuator that opens and closes that flap you see in the big opening that is blocked up. That little pipe connects to the other side of the air box at another little pipe through a vacuum line. That other little pipe on the other side seems to be the thermostat. The thermostat senses temperature inside the air box and opens and closes according to temperature so the flap can open and close. The other side of the air box also has another little pipe on the thermostat that connects to the main vacuum line i believe.
The way it seems to work is the vacuum is always present but is only allowed to reach that vacuum actuator when the thermostat allows it which adjusts the flap (you have blocked up in the picture) to regulate the air temperature inside the air box.
As the flap opens or closes or is part way closed, it allows some fresh air in from the front port or takes in air from the manifold heater part in the back of the engine. The combination of fresh air and heated are is what ends up getting into the air box and so the air box temperature is a mix of fresh and heated air.
That seems to be the way it works on my car. I never got to test the regulation temperature yet though. That can probably be done if you have a spare thermostat. You can run an air line from an aquarium pump to the thermostat and heat the thermostat until it lets air through it. I got an air pump but that was after i reinstalled the air box so i didnt get to test it yet and i dont have a spare thermostat.

Here's a rough schematic...

MainVacuumLine----->-----Thermostat----->-----VacuumActuator----->-----Flap

That's a good explanation of how it works. I don't think your method of testing will work, Though. The pump produces pressure, not vacuum. You would need something like a hand held Mighty Vac vacuum pump for testing.

I did temporarily use aquarium air line for one of the connections on my 850.

Hi,

Cant you just reverse the flow?
The vacuum pulls toward the engine on one of those little pipes that stick out of the air box, and when the thermostat opens that would allow the other little pipe to allow the vacuum to get to the actuator. If you apply pressure to the opposite little pipe (not the one that the vacuum line from the engine connects to but rather the pipe that connects to the actuator) i would think you would feel air pressure coming out of the pipe that connects to the engine main vacuum line. So the pressure is applied opposite to what we can think of as the flow of the vacuum. Once the thermostat opens it will allow air to flow though it and actually i would think it would work in either direction unless there is also a check valve which would allow it to flow in only one direction.
That's the way it should work i would think.

Note it will not operate the vacuum actuator but you should be able to tell when the thermostat opens and closes. You have to disconnect the actuator just concentrate on the thermostat alone as that is what regulates the temperature inside the box.

If you care to try it let us know.

[erikv11]

Turbo P80: viewtopic.php?t=63615
Non-turbo P80: viewtopic.php?f=1&t=65002

[abscate]

You can’t mimic vacuum by applying pressure to the opposite port. You would have to apply it up the opposite side of the motor diaphragm, which has no port to access.

See links above.

We have almost never seen failures in the actual vacuum actuator or the air cleaner box thermostat, just vacuum lines or the elbows seem to be the maintenance spots.

[MrAl]

You can’t mimic vacuum by applying pressure to the opposite port. You would have to apply it up the opposite side of the motor diaphragm, which has no port to access.

See links above.

We have almost never seen failures in the actual vacuum actuator or the air cleaner box thermostat, just vacuum lines or the elbows seem to be the maintenance spots.

Hello,

I am not sure i made it clear what was being tested.
I was talking about testing the vacuum thermostat ONLY, not the entire system that controls the air box temperature.

The vacuum thermostat must be mechanical with a valve that opens and closes depending on temperature. The valve mechanism itself would not care if the flow was caused by a vacuum or a pressure, as long as there was a pressure difference.

With a vacuum the air pressure inside the vacuum actuator would have to be decreased, and to get that to happen we would have to move some of the air particles out of the chamber and that would constitute an air flow with higher pressure in some areas and lower pressure in other areas. The air would flow from higher pressure areas to lower pressure areas.

If we had a garden hose with a pump on the right side that forced water through the hose the water would flow from right to left as the pump pushed water through the hose. If we instead connect the pump to the left side of the hose the water would still flow from right to left but now the pump would be pulling the water through the hose.
If there was a shut off valve in the center length of the hose, if we close it we would stop the water flow, if we open it the water would be allowed to flow. This would be a go/no-go test of the valve.

So what i was talking about was a simple test to see how the pneumatic thermostat worked ONLY in a fairly simple test to see if it worked at all and what temperature it starts to open and/or close at. It would not be as complete as a full system test because it may be hard to deduce intermediate states.

I dont think there would be a comprehensive test for this other than on the car itself because we'd have to know how much vacuum the engine system produces. But then why cant we just use something like a meat thermometer stuck into the air box through a temporary port (drill hole). They make good thermometers that have probes like that we could stick inside the air box and measure the temperature. I think that would be the best way to test the entire system that operates that part.