A/C VENT QUESTION

[Boxcars]

Minor problem -- when I go into any boost, the cold air diverts from the dash vents to the floor, then returns when I've let off the gas pedal. I'm sure this a fairly common problem in our 30 year old cars. Looking for some suggestions of what I might try to prevent this from happening? TIA

 

[regan j]

You are losing vacuum somewhere, Vacuum leak. Light a cigarette and blow into an associated hose and find the leak. Easy Peasy.
Just dont inhale, that stuff will kill you according to the Surgeon General.

 

[Boxcars]

You are losing vacuum somewhere, Vacuum leak. Light a cigarette and blow into an associated hose and find the leak. Easy Peasy.
Just dont inhale, that stuff will kill you according to the Surgeon General.

I don't think that will work. You can usually hear vacuum leaks, and I don't hear any. It's more like the boost is cutting off the vacuum somewhere. Maybe my vacuum hoses are not connected to the right connections.

 

[Boostrules]

Bad check valve?

 

[fitz3820]

I have the same problem, changed check valve but it still happens. I must still have a leak somewhere

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[fitz3820]

Let us know how you fixed it

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[No disintegrations]

I have the same problem, changed check valve but it still happens. I must still have a leak somewhere

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Did you try and flip the check valve in the other direction?

 

[funkyturbo]

Minor problem -- when I go into any boost, the cold air diverts from the dash vents to the floor, then returns when I've let off the gas pedal. I'm sure this a fairly common problem in our 30 year old cars. Looking for some suggestions of what I might try to prevent this from happening? TIA

There are 3 check valves I believe - make sure you get the correct one that goes to HVAC.

 

[salvageV6]

There's a check valve in the vacuum tank itself also.

Put a T on the line out of it and a vac. gauge on it and see what happens under boost.

 

[fitz3820]

Did you try and flip the check valve in the other direction?

Not yet but I will try it. Did the blow test first and it seemed to work

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[Boxcars]

Bad check valve?

Now, this sounds like it could be the problem. Which check valve? Would that be the small one normally located behind the alternator? Not sure I have it on, I'll have to check. I've been changing so many things around for so many years, engines in and out, probably incorrect vacuum line re-connections, and so forth, I may have eliminated that check valve. I'm not sure. To the gent who mentioned the vacuum reservoir, just yesterday I installed one because there was none for years. Previously, it would take a minute or two for the dash AC vents to open. Now, with the addition of the reservoir globe, they open up right away when "max" AC is selected, but it didn't take care of the fluctuating air vent problem. I do have a couple more of these reservoirs. First, I'll deal with the check valve, once I know the one referred to, then I'll switch in another reservoir.

 

[Boxcars]

There are 3 check valves I believe - make sure you get the correct one that goes to HVAC.

Are these all in the engine compartment? TIA

 

[RmvBfrFlght]

The check valve you are looking for looks like this:

It may or may not be faded as this one is. The valve handles the vacuum to the reservoir for the cruise control and HVAC system doors. As for location, check the area behind the EGR solenoid, near the firewall.

RemoveBeforeFlight

 

[Boxcars]

The check valve you are looking for looks like this:

View attachment 281729

It may or may not be faded as this one is. The valve handles the vacuum to the reservoir for the cruise control and HVAC system doors. As for location, check the area behind the EGR solenoid, near the firewall.

RemoveBeforeFlight

I just checked. I knew I had the one pictured, but the small one that sits about 4 or 5" behind the alternator I don't have. I'll put one in there and see if it corrects the problem for me.

 

[RmvBfrFlght]

That may correct the problem as that vacuum line feeds the HVAC & CC check valve.

RemoveBeforeFlight