A/C vents vacuum check valve?

[tlturbo]

Hi all,

I'm trying to find the location of the check valve that keeps vacuum in the lines to the A/C vent doors under the dash when you enter boost mode.

Anytime I go from vacuum to boost readings, I get hot air blowing through the vents. I've been told there is a check valve (not working) that keeps vacuum in the lines, kind of like the vacuum check valve on regular brake systems.

Does anyone know where it is or what it's called? We can't find it in the GM parts book.

Thanks - Terry

 

[S10xGN]

It's the small black/white "cannister" about 3/4" in diameter by 1/4" thick with 2 vacuum hoses attached. It's located just in front off the EGR valve between the DR side valve cover and the injector rail. I just saw them listed in the Poston's catalog...

HTH,

 

[PaulRV6]

VACUUM CHECK VALVE

How should this valve operate? I can blow air thru it in both directions? One way it is slightly restricted but still goes thru. Does this mean it is bad or ok? Thanks

paul

 

[scottyb]

That valve is also available from GM Partsdirect for < 3 clams, not including shipping, 5 and change at the GM dealer. Mine did not stock it.

You should be able to suck air, but not blow(from the same port, that is). When installed, the direction you could suck air should be connect to the intake ports (route). This way it allows vacuum, but stops boost.

 

[PaulRV6]

Thanks, do you know what the P/N is so I can check our GM dealership?
So mine must be bad since I can suck/blow thru the same port. Is that right?

paul

 

[scottyb]

Part Numbers
Vacuum Check valve
My Pontiac dealer had a different one in stock, but had smaller nipples. Computer showed no Gm dealer had one in town.

 

[PaulRV6]

Thanks

 

[Steve Wood]

You might note that the factory chip turned off the compressor at about 80% tps. This would be at 4.0 volts.....I suspect most aftermarket chips retain this value.

 

[basherbob]

Would this also cause the air flow to switch from the A/C dash vents to the floor heater vent? Mine just started switching the air flow under acceleration. Comes back strong when take foot off pedal, high vacuum. Blows cold all the time just out of different vent.

 

[Steve Wood]

It can make it go to the floor...but it will not make it blow hot air thru the vents....the compressor has to turn off to do that.

Of course, I guess if the heater water cut off allows water to flow thru the heater core when pressure comes on, it might blow warmer air. Use some vice grips on the hose to cut the water flow off and try it.

 

[basherbob]

Checked the check valve. Cannot blow through it but can suck air through it. (need to get a life ;^)

Thinking that since it takes a few seconds to switch from dash to heater vents there may be a leak somewhere that allows to system to lose pressure after the vacuum stops. Also hear hissing in the dash but found no loose connections or busted tubes. Can not find source of hissing. Seems to be on passenger side.

Any suggestions? Would this have anything to do with the vent door creaking shut shortly after shutting off the car? Is the diaphragm prone to leaking and is it easily replaceable. Any other known problems of this sort?

Sweating it out under acceleration Bob..............

 

[Pats-GN]

AutoZone has the a similar 2-way check valve in the help section, this fixed my problem for a couple weeks now my vents wont work at all. Good Luck!

pat