If the A/C is manually set to say, 65 degrees, I understand that the center vent should open. Should the defrost/demist windscreen vents stay open or close?

Thanks,

John
1987 XJ-S V12

 

Yes the screen vent should close. Although if the foam has deteriorated you will get air leakage. I get leakage from screen and foot well.

 

Ah, so that's why I have leakage from the screen demist vent when on full cool. Makes sense. What little foam I've found around the a/c has crumbled at my touch.
However, I have full air (not a leak, a blast) from the footwell vents even when on full cool, and always assumed that was deliberate.

 

Yep the blend flaps have foam seals

here are a couple of pics inside my AC evaporator unit you can see I have cut the front out of the plastic evaporator case to clean it out. I should have replaced the foam while I was there but I didn't think about that when I did this 5 years ago.

 

Thanks. I can only imagine what mine looks like inside. Hard to tell where the foam originally went there. Looks like the condenser was covered in it, which doesn't make sense.
I have yet to get onto replacing my core, partially as in summer I only use cooling and so the windscreen isn't misted by coolant, and partially as I haven't had a single free day since the parts arrived, and partially as I need to work out the exact steps to draining and replacing the coolant (including where to get new coolant and how to dispose of old coolant). But I did notice the other day, with the a/c on and the engine still cold, condensed water dripped on the ground under the car (as it's supposed to do, I'm pretty sure: the engine being cool being why it didn't get evaporated by the hot exhaust pipes), and on checking, it was water mixed with coolant. I assume the bottom of my blend box has leaked coolant sloshing around in there....

 

Thanks warrjon, sadly, I was afraid that was the answer.

I've been chasing the wrong problem with my A/C unit (Delanair Mark III). I get virtually no air out of the center vents, so, I "assumed" it was a center vent problem. Actually, I think what is happening is that the defrost/demist flap isn't closing all the way (or has rotted away) and a lot of the air meant for the center vent is dumping out the defrost vents.

Today I concentrated on the defrost plumbing, and sure enough, the solenoid vacuum valve doesn't do anything when power is applied to it. That's partly good news, but the down side is that when I pull a vacuum on the defrost flap actuator (as a properly operating solenoid would do), the defrost flap only partly closes...or closes and, as mentioned above, the foam sealing is rotted away. So a considerable amount of cold air is still ending up going to the windscreen instead of out of the center vent.

Somehow I see pulling the dash out is in my future.

Thanks,

John

 

Unfortunately the vent flaps are deep inside the dash and require the entire dash out, I've been there and kicking myself for not doing it then.

Does the vacuum hold on the flaps or does it leak.

Also centre vent had its own vacuum solenoid IIRC it's the middle one on the right hand side. These are really close to the back of the radio, especially if you have an aftermarket radio that is deeper. The plastic insulation on the connector for the center vent solenoid had deteriorated and shorted to the back of the radio taking out the transistor in the AC ECU.

 

The vacuum seems to hold, and I can hear the flap open and close, but it doesn't seal.

I've checked the operation of the center flap solenoid (it works) and when I pull a vacuum I can make the center flap open and close, of course I don't know if it's opening/closing all the way or not.

I've got the ECU out and have transistors on order, but I suppose I'll have to pull the dash to really sort it all out. Given all I've done to the car in the past 5 years, I guess this is just another step in the Jaguar experience.

I would think the instrument cluster and steering wheel need to come off (I've taken them both off before, so no big deal there) but as for the dash itself I'm not finding much guidance on how to do it. Is there a procedure for this?

Thanks,

John

 

Hopefully these might help

 

Warrjon - I think (think only) there's a problem with the colouring in that diagram you posted. It shows both vacuum restrictors on the right as blue, and indeed, they're listed as the same part in Jaguar Classic Parts' diagram for the XJS. However, having ordered a blue one for my centre vent and finding it doesn't work, I did some digging and found that the parts diagram for the saloon with the same Del Mk III showed different part numbers for each resistor, and hunting down the part number showed the same yellow resistor that has apparently failed in mine. I haven't got around to ordering the supposedly correct part yet, so can't tell for certain, but it's suggestive anyway....


XJS Del MkIII parts diagram. Both resistors labelled as Part 4.



Saloon Del MkIII parts diagram. Resistors shown as part numbers 3 and 4.

 

I had success of some sorts today!

As Some Day suggested, I removed the restrictors, in fact I removed both of them on the right side of the unit (defrost and center vent). Since the defrost solenoid doesn't work, I removed it and plugged the vacuum line directly into the defrost actuator vacuum line...meaning that there will always be a vacuum on the defrost flap actuator, and thus that it should always stay closed. Started it up, put the fan speed to high, and no more rush of air out of the defrost vents , and I get vastly more air flow out the center vent.

Of course the problem with this "solution" is that the defrost doesn't work, but I could care less right now. I have a vacuum solenoid on order (not the Jag part, it's $75), and that should allow operation of the defrost.

One thing I'm not sure about is if I'm supposed to be getting cold air out of the footwell vents. Should those close when the center vent is open?

Given that it's now 93 degrees F, no breeze and not a cloud in the sky, work is suspended for the day. Tomorrow I'll put the vacuum restrictors back in and see if they were part of the problem.

Thanks,

John

 

Excellent new, of some sorts. (I think this is the first time I've actually managed to offer any useful advice. Much gratified, even if it's a stopgap solution.)
Have you tried swapping around the defrost and centre vent solenoids? Just to make sure it is the solenoid that's the issue. You probably have, and I missed it.
As to the footwell vents, I get cold air out there when on Cool, and was wondering myself, but KWE say yes, it's supposed to happen.

First test
Get engine warm
Turn left knob to minimum temp, right knob to Demist. After about 10 seconds hot air should be directed to the screen vents and dash outer vents. Knee vents should be shut.
Turn right knob to medium (9 o'clock position). Airflow to screen should diminish to a trickle, knee vents should open and the air should get cold.
If it is a hot day the centre dash vent should open and yield cold air. If it is a cold day, pull out left knob to Manual (still full cold) and centre vent should open; it takes about 30 seconds.

It's interesting to note that they say the screen vents DON'T shut all the way, merely allowing a trickle. That's exactly what happens with mine, and so I now think perhaps it's by design rather than a problem. Unless KWE somehow don't realise it....

 

A little more experimenting this morning...

Vacuum out of the manifold at idle - 15" Hg.

Vacuum at the reservoir outlet 14.5" Hg.

Vacuum at the servos - 14" Hg.

I put the restrictors back in line, and the system operates as it should (minus the bad solenoid), defrost vent nearly completely closed (just a slight leak, and maybe that is be design)., and much more air coming out of the center vent. So I'll propose the theory that taking the restrictor out gave some "umph" to the defrost flap actuator, clearing the jam or whatever was keeping it from fully closing in the first place.

I didn't swap the solenoids, as there is no doubt the defrost solenoid is bad. When I put 12 volts on it, nothing happens, no noise, and it doesn't open to let air through. New solenoid should be here tomorrow so I'll know soon enough.

I really don't like cold air coming out of the footwells, I'm going to play around and see if I can get the lower blend flap to close when the A/C is on.

Thanks again for the idea!

John

 

Getting the cold flap to close when the ECU wants them open will probably involve a bit of wiring and a secondary switch so you can override the ECU command. I've seen something similar on a Japanese XJS website for controlling the recirculation flaps so that when in traffic you're not always breathing the fumes of the cars in front.
Great that the system works with the restrictors back. Can you confirm the colour of the centre vent restrictor, please? Is it yellow (white and yellow)? See what I mean at: My Recent Thread On Restrictor Issues.

 

The blend flaps are not driven by vacuum like the recirc flaps. The blend flaps are servo motor driven with a position sensor on the other end. To run them manually you would need to drive them with 12volts while disconnecting the ECU.

 

In my car, the center vent restrictor is blue and white. In fact, both the restrictors on the RH side of the unit are blue and white. Actually, if I recall correctly, all the restrictors in mine are blue and white. I'll confirm that when the rain stops.

I replaced the defunct solenoid valve with a much less expensive generic unit (around $9 from Amazon, compared to $75 from the usual Jag part dealers). The system worked, but for whatever reason the defrost didn't shut down as completely as it did with the restrictor in place, so I removed it.

Hmm...maybe trying to shut down the footwell vents when the A/C is on is a bridge too far. By the time I pull it off it might be winter again :-)

Thanks,

John

 

The footwell vents are not vacuum operated, the lower blend flap in the Evaporator is also the footwell vent control

 

Thanks for checking.
Hmm. That suggests that the restrictor isn't in fact the problem in my system. I suspect the flap might be just sticky enough that while it opens with full vacuum applied immediately, the gradual change of the restricted vacuum isn't enough.

 

Or there is a leak in the actuator, the restrictor will drop the vacuum at the actuator, if there is a small leak there may not be enough vacuum to fully move the actuator

 

Thanks for that. Could be. Noob question: what's the actuator? Not the solenoid, right? I'm not sure of the difference. If it's the solenoid, I remember the mechanic pulling it, replacing it with one from another XJS, and that not fixing the problem.