[02Pilot]

It seems I have developed a small vacuum leak at or near the air distribution valve. I reseated the connector on the back and made sure that the securing ring is latched top and bottom, as well as inspecting the hoses, which seem to be tight and in good condition. The leak is audible, but does not seem to be affecting operation of the valve. In the top two positions - floor/defrost and defrost - the leak stops; in all other positions it remains, though perhaps at slightly varying intensities.

Am I right to think that this is likely a problem with the valve itself? Are these valves rebuildable or repairable, or is it simply a matter of finding a good one and replacing the existing unit? Thanks.

 

[jvanabra]

I have had this problem too - it's sometimes the knob itself and sometimes it's the vacuum hose "harness." I have not been successful with repairs, but TBH I haven't tried that hard. In the past, it's been a junkyard trip... next time... I don't know.

 

[02Pilot]

I suppose a smoke test would be the definitive answer as to the source. Assuming it's the valve itself, my curiosity may lead me to buy a good one (eventually - I've already spent too much on this car in the last three months) and take apart the old one to see exactly how it failed.

 

[Jim Mesthene]

Am I right to think that this is likely a problem with the valve itself?

Based only on my observation of their failure rate, I'd bet dollars to donuts the valve is fine.
Defrost is the default position with no vacuum. Any loss of vacuum in the system will push it to revert to defrost.
Squirt the valve with water, see if the noise changes.

 

[02Pilot]

Based only on my observation of their failure rate, I'd bet dollars to donuts the valve is fine.
Defrost is the default position with no vacuum. Any loss of vacuum in the system will push it to revert to defrost.
Squirt the valve with water, see if the noise changes.

Can you clarify what you mean by "no vacuum"? The vacuum supply into the valve via hose #1 is constant; the diagram shows hose #4 going to the defroster. Do you mean that the defrost vents default open and are closed by applying vacuum?

 

[jvanabra]

Yeah, that's correct IIRC. That way if the system fails you still get to see out the windshield.

 

[02Pilot]

OK, got it. So now the question is why the sound of the leak goes away when the valve is turned to defrost.



If I'm understanding the system correctly, defrost requires no vacuum, so when turned to that setting, I presume the vacuum supply is cut off at the valve; this leads me to believe that the vacuum source is not the point of the leak.


That the vacuum leak is audible in all the other positions suggests the leak is not in any of the component hoses, as if it were the leak would only be heard when that hose was connected to vacuum.


So I'm left thinking the problem is either in the connection between the valve and the plastic hose octopus, or in the valve itself. I will pull that half of the fascia away again, spray some water on it as advised, and see what happens. If I can't determine anything, I may try to lightly pressurize the system and spray it with soapy water to see if I can spot any bubbles.

 

[jvanabra]

So I'm left thinking the problem is either in the connection between the valve and the plastic hose octopus, or in the valve itself.

Yep, that's the typical two scenarios IME. You may learn something by just removing the stereo and holding the octopus to the valve to see if that stops the leak. It'll give you a clue about where it is before taking things apart.

If you're dexterous, you can remove the valve without taking anything but the radio out. Just a couple small screws frees it from the knob.

 

[02Pilot]

Yep, that's the typical two scenarios IME. You may learn something by just removing the stereo and holding the octopus to the valve to see if that stops the leak. It'll give you a clue about where it is before taking things apart.

If you're dexterous, you can remove the valve without taking anything but the radio out. Just a couple small screws frees it from the knob.

I tried pressing on the octopus, both with the retaining ring in place and removed - it did nothing.


I'm pretty good working blind in small spaces, so I'll see if I can pull the valve that way first. I've had the fascia off at least four times in the last few months, so it's not the worst thing in the world if I have to pull it again.

 

[02Pilot]

Just to close this out, here's the resolution. I pulled the dash fascia and the valve, then disassembled it. It's really simple, with two electrical switches that just lift off, and a plastic rotating assembly that is pressed by a spring on to a rubber piece with channels that distributes the vacuum; this is all retained by the steel backing plate, held on with two screws. Aside from a little cleaning, I saw no issues with the valve itself. I started testing the lines coming off the octopus and found that #4 was not holding vacuum. I traced this back and found a tiny split at the servo end. I cut this back, reattached, and it held vacuum. The location of that servo, which feeds the defroster vents, is right behind the valve, which is what made it seem like the valve was the source. It's fixed now.