Finally dug into it today. Bypassed everything except the vacuum hose leading from the center vent actuator. With the glovebox out, I can get my hand around the back of the actuator just to feel the mechanism. When I pull a vacuum on it, it *wants* to move, but doesn't. When I pull a vacuum and stick my other hand into the vent I can help it move a little. I can hold the vacuum quite a while, so it doesn't seem to be vacuum leak related.

I see of no way to get to that area without removing the dash. But, just in case, I wonder if anyone has a photo, diagram, sketch, or something else that resembles how the actuator connects to the flap. If I could figure that out, and figure out if there might be something I could do by cutting into the dash a bit (where the wood trim would cover the hole) I might give that a try.

Thanks,

John
1987 XJ-S V12

 

If you have a delanaire mark II (your car date is about the change date) then I think that all the flaps are activated by levers and rods on the RHS (US Passenger side). These are accessible if you remove the RHS cheek on the console - the one with the footwell vents. They are sprung in one direction, but they can be moved to change the flaps position.

 

Sorry Greg, I should have mentioned that mine has the Mark III unit.

Thanks,

John

 

Out of curiosity, have you tried removing the vacuum restrictor for the centre vent? I had a problem where the centre vents wouldn't open up, and it was solved (provisionally) by removing the restrictor and plugging the vacuum hose in directly. I suspect the flap's a bit gummed up and the slight loss of power from going through the restrictor is just enough to prevent it moving.
Just a suggestion from my experience. I'm just not sure what you mean when you say you "bypassed everything except the vacuum hose leading from the centre vent actuator."

 

What I meant was that I took the ECM and solenoid vacuum valve out of the equation simply by bypassing them. I took a piece of vacuum hose, plugged it directly into the line that leads to the center vent flap actuator and put a vacuum (sucked) on it, just to see if it would open and close. It does, but of course since I can't see it I can't tell how much it is opening or closing, or how much of the sealing material (foam I guess) is gone.

Having said that, I like your idea. Nothing to lose by trying it.

I'll report back...and thanks.

John

 

You will need much more vacuum than sucking with your mouth to move those flaps. I used a syringe and it worked well.

 

Thanks for that. The question is, how much vacuum is "enough"? Looking through the "Mark III Climate Control" manual, and the "Delanair MK III Air Conditioning Service Introduction 1987 Moden Year" (what a title!) they are both mute on the topic.

I suppose I could measure the vacuum and idle and assume that should be enough. Time to buy a vacuum gauge I suppose.

Thanks,

John

 

The centre vent AIR flap will not open until the upper BLEND flap is in full cold position and the upper blend flap position feedback pot sends signal to ECU to allow vacuum feed.
It may be that your upper blend flap is actually your problem and not the centre vent itself.
Mine was gummed slightly from degraded foam and dicey servo. I cleaned foam as best l could with probes and swabs in through front centre of unit and servo came good with a couple of raps with a screwdriver handle.

 

Yes, I suspect, based on the pics of the interior of his that Warjon posted, that there's a fair bit of gunk up in there, and a good cleaning is probably the place to start before chasing vacuum issues. I should remove the front vent and see if my cheap Chinese boroscope can shed any light on the problem. It's a pretty convoluted path from there, I believe....

JCR - I have no idea if this will fix your problem, but it's a very simple test anyway as long as you've got solenoid access. And you should be able to feel a bit of a vacuum by holding your finger against the solenoid hose end with the a/c on cool. I'm not sure I'd call it "strong" (which might be part of my issue), but it's certainly there. I like the syringe idea actually. I might find one suitable to test. I assume you put the a/c on cool, pull the tube from the solenoid, and use the syringe to suck and see if the parts operate as designed.

 

I think the problem is more likely to be blend flap malfunction rather than centre air flap. The condition of the vacuum actuator for the centre flap is irrelevant if the ECU is not signalling the solonoid valve to allow vacuum supply to it.
l would start by attaching a vacuum guage to the valve feeding the centre flap (black tube R/H side valve block) to see if any vacuum exists when it should, (ie. full cold selected) if not your centre flap problem is more likely a symptom of a blend flap/ECU problem rather than a cause.

 

Thanks for all the above. I have a hand-operated vacuum pump and a vacuum gauge, on the way. Will try the above and report back.

I have an old gooseneck inspection camera that I ended up with somehow. I've never had an occasion to try it, so I don't know that it works, but I'll hunt it down today and see what I come up with.

Thanks,

John

 

Some what related question. How do you remove the A/C Temp control knob. The Fan speed switch knob just pulls straight off. But I can't get the Temperature rotary knob off.
Is there a set screw? Do I squeeze the shaft? Or am I just not pulling hard enough. I'm sure it's an expensive switch and I don't want to break it.

 

I'll be back working on mine tomorrow ('87 with the Mark III), and will take an look since I have both the floor vent assemblies off.

Thanks,

john

 

They should both pull straight off.

 

Ok, see attached photo. So much for memory. On the LH side of mine, there is a red/white restrictor on the recirculation vacuum solenoid, and no restrictor on the water valve solenoid (also known as the "coolant valve solenoid), which, according to the Mark III Climate Control document, is correct, i.e. there shouldn't be a restrictor there.