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Old 08-12-2017, 06:26 PM   #1
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Default Help in diagnosing HVAC Vacuum Actuator part.

Hello all

First time post here.

So I have a 2002 Blazer Zr2 Blazer with about 75 k on it and it'* in pretty good shape.

Recently I had the heater core go so brazed up a bypass out of copper fittings while I get all the parts together to repair.

Since this will require pretty much taking the whole dash out I figured I would get to a long put off repair where there is some kind of vacuum leak for the controls in my HVAC system, but so far I have not been able to pinpoint it as never wanted to go this far.

Currently if I have enough engine vacuum say as its at idle or low RPM, all my vacuumed controlled parts generally work correct. But say when I get in the highway or at mid to upper throttle, they all loose vacuum hold and things start coming out of every vent.

Just to mention, this all came about years ago as I had that thing where my 4wd transfer case vacuum switch sucked up fluid and it got into the dash controller for sure and I think I pretty much have it all out of the system now but something is still leaking and I also have replaced the vacuum control **** cluster a couple of times so am pretty sure that is not the source.

Anyway, I figure since it would be all apart I would just replace all that is there as why not and have been trying to hunt down the parts but it has not been easy as apparently most of them have not been made for sometime.

But I have got most of the vacuum actuators and doors all but one which is what is generally called a Slave Door Actuator PN: 52489533 which I just can't find anywhere.

Oddly as this one can be gotten too by just releasing a spring for my glove box door, I was able to get to it and so I put a hand vacuum pump on it today an sure enough it really would not hold much Vacuum

Now just to mention, this one has a spring return on it so this is really where I get to my question which is...is it normal that it will actually leak somewhat, or does anyone think they are supposed to hold solid.

Basically I can pump it into a Vacuum well into 300in Hg, but it will drop back from that to about 100-80 fairly quick but the valve does not try to return. From that point it sit there and the vacuum will slowly leak away after 2-3 min while the arm slowly creeps back. Eventually after almost 5 min it is fully returned by the spring.

So again, is hard to know if this is normal or is there basically a accepted leak amount as its not like its on the space shuttle or something and really even with this amount, it should not be enough of a leak to allow all this to be happening, or could it actually be the problem.

Know it'* a bit of a guess here, but any help from previous experience will be much appreciated

Thanks greatly.
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Old 08-12-2017, 09:59 PM   #2
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Could be a leak, or even something as simple as a bad check valve.....

Do you smoke?.....no, find someone who does........have him blow into the main line off the intake, and look for smoke coming out somewhere...
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Old 08-19-2017, 08:29 AM   #3
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Quote:
Originally Posted by Tech II View Post
Could be a leak, or even something as simple as a bad check valve.....

Do you smoke?.....no, find someone who does........have him blow into the main line off the intake, and look for smoke coming out somewhere...
Thanks for the suggestion Tech II.

Yeah, have working on this and so far have found two major leaks, one was the rubber hose and its connection to the somewhat hidden vacuum reservoir in the fender. The other was a major actuator failure which was from the defrost actuator.

That actuator was one that finally came in this week and upon seeing how much it was to replace I found at least I didn't have to remove the dash but just mostly its lower cover and the console.

Once I got those out I checked the actuator with a hand vacuum pump and it was completely shot.

As it is a push pull one when I got it out I found I could completely blow from one side and have air come out the other.

Just to mention, in the testing of all the actuators I have gotten new so far, I have yet to find one that lost any vacuum air at all, so I have to suspect in regards to my original post, that the one I have that leaks a tiny bit is not normal and since I can't get a new one I guess the only thing to do it leave it as it is an hope it doesn't get worse any time soon.

Anyway, in getting everything back together my defrost control and many of the things work much better now although not 100%.

The only vacuum actuator I have yet to be able to check is the mode one as its just to buried to get too, but as its a push pull one too I suspect its not in great shape and probably why I am still not 100$, but I do have a new one of those so will replace it when I do the heater even if it tests OK as since I can't get to it any other why makes no sense not to.

Only think I am waiting on now is the foam that is supposed to go around the heater core which I have to think is bad.

For all my searching I could not find this part except for one non auto-vendor who said they could get it, but it has been a few weeks now and the order has not been completed so I am not holding out much hope.

Anyway, will make a separate post for that.

Thanks again for the help.
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