captcashew

So, I've found that the center comb flap actuator and my footwell flap actuator don't seem to be holding vacuum. I was looking at Dwayne's instructions on what he did on his 87 and sounded about the same as the issue I was having. So as part of those instructions, it mentions to test the solenoids. I wanted to make sure I was clear on exactly how I go about testing this. When I cap each of the solenoids and vacuum test at the main entry of the manifold, it doesn't hold vacuum.

So I assume that means one or all the solenoids are bad. When I test each one individually, I'm just supposed to test the solenoid at the corresponding HVAC head unit setting to that particular solenoid, right? Because I assume if I'm on the wrong one, it won't hold vacuum.

Are there any more detailed instructions out there?

docmirror

Yes, there are much more detailed instructions out there(here). Including pictures and diagrams. It's unlikely that all of your solenoids are failing. The solenoids are not usually the failing component in the vacuum HVAC system. Far more often it is the diaphram inside the actuator which gets a pin hole, or a crack and will not hold vacuum.

Test your actuators with a small mighty-vac, or you can use your mouth. I'm betting you'll find many of them bad.

westija

Yes, and remember to cap each solenoid (with vacuum plugs) and test them individually without the manifold.
As you test the whole thing (manifold and all solenoids together) and find leaks you then have to test each individual component to pinpoint the root cause. I agree is very unlikely you have all solenoids leaking.

When I tested mine I found two bad solenoids and the manifold leaking.
Replaced the solenoids and re-tested and they were fione. Bought a used manifold but it is also leaking (am placing a new order this week).

Good luck

captcashew

Yep, I already tested the vacuum hoses to the actuators. The footwell and center comb didn't (orange and yellow) vacuum. But as a follow up, I figured I'd test the solenoids. I'm concerned about my manifold as well. The pulled the manifold out entirely and tried sealing the 5 hose holes and testing it and it seemed like it had a very slight slow leak. WHere are you ordering yours from? Do you have a part number? I looked at the catalog and couldn't find that. (found the solenoid part number)

When I did a main test of the solenoids (using my mightyvac and some vacuum caps), it was leaking, so then I did each solenoid individually. I was seeing either major immediate leaks right away or very slow leaks. But I'm not sure I had the settings on my HVAC head unit set correctly to test. That is why I was looking for some instructions that are specifically detailed about vacuum testing the solenoids.

westija

Mine is a '89 S4 model. Parts Manual (PET) Page 313 item 20 - 928 573 695 03 - Connection.
Not sure if it is the same for yours, but would think they are all the same.

In terms of testing the solenoids, it might be that you have all bad, but it is unlikely. The caps might allow some air to enter indicating a vacuum leak. Since you are finding all bad anyway, you might want to remove each solenoid from there and test on a more convenient place (with plenty of light and space) before you order them, just to be sure. Dwayne mentioned in one of his, he found 4 out 5 bad.

Finally, for the footwell flap bladder / diaphragm, take your time and be patient to re-install the lever. Dwayne mentions a hole thru the plastic panel to help. I found this website below very helpful (pix quality not that good but good material, indeed). Take your time and enjoy.

http://jenniskens.livedsl.nl/Technic...ACproblems.htm

captcashew

Thanks, that part number seems to be the same. One less thing to track down.

Yeah, my vacuum tester had been really solid up until the solenoids. I was concerned there was a minor leak from the pump somewhere. Just to be sure, if I cap one end of a solenoid, then attach the pump to the other, without turning the car on, should I be able to draw a vacuum? Or will that only be when the ignition is turned on and the HVAC head unit is set to certain settings? A couple of the solenoids I don't get any vacuum. Others I get a little with a slow leak (takes maybe 20-30 seconds to lose the 10 inches of vacuum).

captcashew

OK, I borrowed someone else's hand vacuum pump to make sure I was getting accurate results. The chart below shows what I got.

I tested each solenoid individually. I put the pump where the manifold would go and a vacuum cap where the colored vacuum hoses would be. Then pumped them up to about 15 inches of vacuum and tested between 1-2 minutes at off, then for each of the 6 HVAC head unit settings.

So, now I know the results. But what does that mean? Is it ok that certain solenoids lose vacuum at certain settings? The only one that passed every stop was the yellow solenoid (footwell flap). Can anyone help me interpret them?

Alan

Consider that your car generates vacuum all the time its running and not at WOT - you also have a vacuum accumulator (vacuum store) and a one way valve to the vacuum source.

If you have a total accumulated vacuum leak that leaks away in ~1 minute how likely is it that you will stay at WOT for more than 1 minute?

Now once you have leaks they are only likely to get worse - but aside from possibly a little hissing noise you probably would never notice these minor leaks until they get worse.

However once they accumulate to leakdown in just a few seconds - then your flap positions may modulate every time you hit WOT for any reasonable period... this is very annoying and when the vacuum leak reaches a sufficient magnitude that flap (and possibly the others too) may never activate at all...

Alan

captcashew

It must be getting late in the day, but my brain isn't clicking on what WOT stands for.

StratfordShark

Wide Open Throttle (forgive me for jumping in) when there is much lower inlet manifold vacuum.

I tested my solenoids on the bench - much more comfortable! Just undo the single screw holding each solenoid cube to hvac manifold. They were all fine. As another poster has mentioned leaks are more likely in the catuator diaphragms.

captcashew

Ah, that makes sense. So what you are saying is that don't sweat the small leaks that don't lose vacuum right away. Which it seems like almost all my solenoids are more or less ok. I definitely do have leaks in the actuator diaphragms of the center comb flap and the footwell flaps, although the footwell is slower, still significant compared to what I am seeing when testing the solenoids. So those are the major concern. I'm not 100% since I haven't ripped out the old actuators yet to check, but all signs point to that being the case.

Is that an accurate assessment of what you meant?

Yes, testing on the bench would have been more comfortable, but I was wearing knee pads, so it wasn't as bad as it could have been.

Kevin in Atlanta

I have what I think is a faulty AC solenoid for my hot water valve(HWV). Used vacuum tester at the HWV and going to the HPV from the solenoid - have vacuum and HWV will close. No vacuum coming from the solenoid with the car on. Solenoid will not hold vacuum with the car off.

Have I done the requisite testing to isolate the fault at the solenoid?

-Kevin

StratfordShark

Hi Kevin,

Sounds like your water valve actuator and line to it are ok, but under the temp context at time you tested vac from solenoid it just may not have had vacuum switched through it.

The best way to test that solenoid is as described earlier. Get the manifold out (one or both carpeted sides slid off, then undo machine screws at each end of manifold and centre. You'll need to slide radio back a few inches for access or remove it.

Then you can take off each solenoid and test on bench. I don't recall whether they are meant to switch vac through with no power applied or not. If they are normally open then I would have used a small battery to power them and then tested whether they held vacuum. I do remember playing with battery just to see if they clicked and electrical side was working.

Kevin in Atlanta

My assumption is there should be vacuum to the hot water valve unless you are trying to heat the cabin. If I get no vacuum at start-up or the white line to the solenoid does not hold vacuum with the car off the solenoid is faulty, right? I would think with the car off and no signal to the solenoid that the solenoid would be in the closed position and therefore hold vacuum.

merchauser

Bumping this post; need a little help/advice.

I have read and re-read as many posts regarding the HVAC and still not grasping certain elements

Dash is apart to repair some leaking actuators and have the solenoids out for bench testing. 4 of the 5
leak down from 25 to 20 in about 20 seconds, then down to 15 in another 20 seconds. The fifth one was
clearly bad leaking down from the start.

in post #8 Alan said Watched Erik's (Hacker) you tube and it seems vacuum should hold, although, he didn't leave the vacuum
connection connected that long.

Should the solenoids hold vacuum indefinitely when they are new?? Prefer to get these spot on proper rather
than dig them out again. Could ALL 5 be bad?