WICruiser

Got it, thanks.

The Combo flap was just hard to see, dark in there but the drilled hole made it easy enough.

The link connecting the defroster flap on the right side popped off when i was polking around in the air box through the right side hose connection and I could not get it reconnected. I ended up pulling the back side of the air box off - once you are this far into it (I had the pod off already also) the dash is not that much more to gain access. It turns out that the defroster link comes from the inside of the two flaps that it is connecting because there are ribs on the outside that interfere with the engagement of the plastic connectors. Once I got into the air box it was pretty straight forward.

Thanks again Dwayne for great write up.

Manfred

Hey Dwayne (or anyone else),

I just did this procedure on my 91'GT. It appears all five of my solenoids are leaking and also my center comb flap (orange line) and the heater valve (white line). I just wanted to check to make sure I was doing the test correctly before ordering the replacement solenoids. When I plug my Mityvac directly into the solenoid ports they all suck air in from the hole in the bottom of the solenoid (power off). Some of them will hold pressure if I place my finger over the hole. With the power on I can't get any of them to hold pressure under any situation, even with my finger over the hole. So I'm right in assuming all five of my solenoids are bad, right?

Dwayne mentioned he ordered used solenoids from Roger; anyone have any opinions on used vs. new (I don't really know anything about how they work/their mode of failure)? Since my '91 seemingly has five bad solenoids it appears these wear out with time. Heck, I stand a good chance of buying used solenoids that are older than those in my '91...

Thanks,
Dan

Hilton

Manfred, you shouldn't be measuring vacuum against the solenoid manifold (where all the coloured lines converge).

You should be connecting to each coloured line directly and then seeing if the end of it not connected to that manifold holds vacuum.

I use a spare rubber elbow from a vacuum connector to aid in getting the mity-vac attached to the hard plastic coloured lines (if you don't have a spare you can borrow one from the vacuum valve for the charcoal cylinder or air pump diverter valve).

Its highly unlikely that all your HVAC actuators leak.

Hilton.

Manfred

Hey Hilton,
Yeah, actually I did do that too, sorry if I wasn't clear. Doing what you described I found I'm leaking at the center console actuator (orange) and the hot water valve (white). Dwayne also recommended testing the solenoids after testing the individual lines and associated actuators by connecting directly to the individual solenoid ports (where the hard colored lines exit the solenoids towards their respective actuators--that's where I can't get any solenoid to hold vacuum, either with the power on or off.

Dan

Dwayne

Hello Dan,
It's best to test with an air tight cap on the solenoid rather than using your finger. Do you have any of the vacuum caps like the ones in the picture earlier in this thread?? If you're sure you have an air tight connection on the input port and output port of the solenoid under test and you are still getting leaks (loss of vacuum), then I would say the solenoid is leaking. Four out of five of my solenoids were leaking on California (the '84) while all solenoids were working fine on Virginia (the '87). However, my leaking solenoids only leaked when power was applied. If you closely inspect the base of the plastic nipple on the solenoid (where the vacuum hose is attached) you may see discoloration or cracking. On California, I saw the discoloration at the base of the plastic nipple and it looked like it was brittle and a possible failure point.

I actually ordered my used solenoids from 928 Intl but I'm sure Roger has them too (and probably 928 MS and 928 WW). I was concerned that the used ones might leak as well but they came with a guarantee not to leak (for 90 days, I think). When I received the used solenoids, I tested each one and all of them worked with no leaks.

Manfred

Hey Dwayne, I think I misunderstood the first time around. I was plugging the mityvac into where you have the ports capped and was getting leaking from a hole in bottom part of the solenoid. I'll repeat the test as described and report back. I do have four vacuum caps (not five) but since I'm testing one a time I only need one, right?

Another question you may have input on: it appears that failure of the hot water valve (white line) results in a heat always on condition. I can't get vacuum to hold on the white line but my heat and AC work fine--or at least I haven't noticed that my heat is always on (I generally have my fan setting at 0 unless I'm using my AC so maybe I wouldn't have noticed if the cold air from the AC is overriding the hot air? In any case, I'll be pulling my airbox and directly testing the hot water valve so maybe the answer will be clear.

Is the hot water valve something that can be pulled apart to inspect the diaphragm? I'm thinking maybe not since it looks like when it's bad the entire part is replaced, not just the diaphragm.

Thanks,
Dan

Dwayne

Hi Dan,
Yes, since you are testing one solenoid at a time, you just need one cap. I used 5 initially to test the whole assembly but when I found I had leaks, I had to resort to individual testing to pinpoint the bad actors. Also, after pulling the vacuum and turning on the ignition (but not starting the car) you find that the solenoid is holding vacuum, operate the air distribution slider (lower slider ****) to excercise the solenoids. If it still holds vacuum, the solenoid should be good.

You are correct in that the default position of the heater water valve (i.e., no vacuum) is wide open. This means hot engine coolant is allowed to flow to the heat exchanger in the dash. Even with a leaking diaphram at the heater water valve, the vacuum line to the valve is under constant vacuum when the solenoid is directing vacuum to the valve. So as long as your valve moves when vacuum is applied (even though it may not hold vacuum), there may be sufficient vacuum to hold the valve shut if the leak is small. This may be why your A/C still works even though your heater water valve doesn't hold vacuum (assuming the leak is small enough).

However, under certain conditions, like driving up a long uphill grade where you have open throttle and low vacuum in the intake, the vacuum reservior will eventually deplete through the leaks in the HVAC system (e.g., at the hot water valve). When this happens, after a short period of time, there's not enough vacuum to hold the heater valve shut and it will open and allow warm water to enter the heat exchanger. If you're running the A/C, the result will be the A/C will get warmer. Let off the gas or coast down hill for a short distance and the vacuum will build in the reservoir and the valve will close and the A/C will get cold again. This phenomenon happened to me on California until I fixed the HVAC leaks.

As to pulling the diaphram apart for inspection. I have not tried that (others may have). I performed two tests on the vacuum diaphram: 1) the vacuum test as you are doing and 2) a coolant leak test. To do the leak test I removed the valve assembly then poured water in the intake side while holding the assembly vertical (intake on top and output on bottom), applied vacuum, and watched to see if water came out the bottom (output side). I believe I have a picture of this in my '87 Intake R&R thread. Sometimes the diaphram may hold vacuum but the valve itself may have a small leak allowing warm water through to the exchanger. I ended up simply replacing the valve/diaphram assembly - it was cheap.

Hope this helps.

Manfred

Hey Dwayne, Thanks for the detailed reply. I'm fresh in from the garage with my latest test results.

I have one bad solenoid (footwell) when I do the test appropriately!

The vacuum leak in the hot water valve is pretty big in that there isn't a slow leak of vacuum--it won't hold anything at all. I did have my wife pump the mityvac (attached to the white line from the center console) while I watched the valve and it will move about 1/2cm so maybe under constant vacuum that's enough to at least slow the flow of hot water somewhat. I also pulled the white vacuum line off the hot water valve and capped it and applied vacuum to the white line at the center console and the vacuum holds so I know there's no break in the white line somewhere hidden in the firewall area.

So, my shopping list is pretty easy: one center console actuator diaphragm, one solenoid and one hot water valve. Thanks for your help, Dan

Tony

Thanks for that pic Dwayne!!!

6mil928

That picture ROCKS

Charley B

Another great write up Dwayne. I especially appreciate the extra detail and pictures that you routinely provide. They allow even a bumbler like me to wade through the instructions without getting lost.

Tony

right now my HVAC is...
heater valve tied shut...
Recircflap opens whenever engine is on
Center combflap full open/up. Diagphram is shot so it is manualy set it full open. Thus, less restictive flow out of the center vent and quieter.
I also have a layer of speed tape over the "grates" that discharge any warm air passing through the heater core.

Living in vegas ,in the summer i dont have to worry about humidity and cool summer nights///foggy windshields etc etcs.. All i want is cool air. period..

All can be back to stock in about 20mins

6mil928

I'll be zip tying my heater valve shut soon as well.

Alan

Tony - doesn't that sometimes make you too cold with the AC on?

Alan

86'928S MeteorGrey

DUDE. You are awesome. I'm sure you've heard this before. I've spent a lot of time checking out your posts and "Dwayne's garage". Have you thought about publishing a book with all of your step by step photo laden proceedures? I for one would buy two. One for the coffee table, and one for the garage. If the WSM were half as clear as your repair proceedure walkthroughs, the 928 would still be worth premium money, and I wouldn't be able to afford one!

KEEP IT UP O MASTER OF ALL THINGS TECHNICALY PHOTOGRAPHED!!!!