[xj40] No air in center vents

92 xj6 with 92k

I have done some minor work on this vehicle in the past
and just recently purchased it when the owner decided to
get rid of it.

I have done some searching for the vent issue that I’m
having but haven’t found a detailed fix at this point.
Didn’t know if I’ve missed something or if it hasn’t been
made available.

The center vents produce virtually no air regardless of
the climate control settings. From what I have read, it
may be a demister vent failure? If so, I’m not sure how to
go about fixing it. I have just purchased the Haynes
service manual but don’t know if it will be of any help.

Any thoughts or direction would be appreciated.

Thanks–
dtrain
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In reply to a message from dtrain sent Wed 1 Aug 2012:

Center vent is a very common problem.

Most commonly is the vacuum module pops apart
from internal spring pressure. You can remove
the spring and use silicone as an adhesive and
sealant. The front wood trim pops off and the
louvers slip out.

Also possible the module simply has a vacuum
failure. Remove the glove box to check the
lines and solenoid.–
The original message included these comments:

I have done some searching for the vent issue that I’m
having but haven’t found a detailed fix at this point.
Didn’t know if I’ve missed something or if it hasn’t been
made available.


97 Sov, 02 VDP – Driveway’s got too many SAABs in it!
Tampa Fl, United States
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In reply to a message from dtrain sent Wed 1 Aug 2012:

First of all, are you sure that BOTH A/C blowers are working?

Are you aware that the centre vents are normally closed and
only open with vacuum when A/C is selected?

If, after selecting A/C with both blowers working you get
great volumes of air out of the demist vents, then the
demist vent vacuum operated flaps are stuck open. They are
normally held closed by vacuum unless Demist/Defrost is
selected.

If the demist vents are broken, you need to remove the
entire dash to get access to them for repair or replacement.
Follow the link in this recent post and try the HVAC test
procedure to further narrow down the fault(s).

http://forums.jag-lovers.org/tv.php3?zx=SdAHzRPwx6MOPMsJ9NmjxwfMCwKandD4%2BkRB06PNM9AO%2FsidzgTHSQacns8LERIHl5jJCshRBJmWxgLJCy%2BIoQ%3D%3D--
The original message included these comments:

The center vents produce virtually no air regardless of
the climate control settings. From what I have read, it
may be a demister vent failure? If so, I’m not sure how to
go about fixing it. I have just purchased the Haynes
service manual but don’t know if it will be of any help.
Any thoughts or direction would be appreciated.


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Wed 1 Aug 2012:

Thanks for all the input. I was unable to open the link that
you left in your reply. I tried clicking, copying and pasting,
etc. but nothing came up. It keeps saying that my session has
expired or that I’m not logged in… Any ideas?

thanks–
dtrain
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In reply to a message from dtrain sent Wed 1 Aug 2012:

Yes, so it does to me too! I really don’t know why, but this
is the text I was directing you to (assuming that BOTH
blowers are working) :-

HVAC system try this test:-

With the engine up to normal operating temperature, set the
temperature control knob on the panel to ‘Full Cool’ in
‘Manual’ mode with the fan speed on ‘Defrost’ (nothing else
selected)

You should get:-

  1. Hot air at full volume out of the DEMIST vents
  2. Some air out of the SIDE face vents
  3. NO air out of the CENTRE face vents
  4. NO air out of the FOOTWELL vents

Turn the fan speed control to ‘High’.

After a delay of, perhaps, 45 seconds, you should get:-
5) NO air out of the DEMIST vents
6) Cold air out of the SIDE face vents
7) Cold air out of the CENTRE face vents
8) Cold air out of the FOOTWELL vents

Turn the temperature control knob to ‘Full Heat’

After a delay of, perhaps, 45 seconds, you should get:-
9) NO air out of the DEMIST vents
10) Hot air out of the SIDE face vents
11) NO air out of the CENTRE face vents
12) Hot air out of the FOOTWELL vents.

NOTES:

  • The ‘45 seconds’ delay is to allow the ECU / system to
    react to the new selection - and to avoid ‘hunting’.
  • You can REDUCE the temperature exiting the face level
    vents in relation to that exiting the footwell vents by
    moving the slider control from ‘hot’ (temperatures the same)
    to cold (face level cooler)
  • You can introduce demisting by selecting the ‘AIR’ button
    on the panel
  • You can alter the dehumidifying effect of the A/C by using
    the ‘raindrops’ buttons or cut out the A/C compressor
    completely by selecting ‘ECON’
  • In ‘Auto’ mode (not ‘Manual’) the ECU varies the fan speed
    on ‘Low’ and ‘Medium’ only but not on ‘High’ or ‘Defrost’.

Post results 1 to 12–

The original message included these comments:

Thanks for all the input. I was unable to open the link that
you left in your reply. I tried clicking, copying and pasting,
etc. but nothing came up. It keeps saying that my session has
expired or that I’m not logged in… Any ideas?


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from Bryan N sent Wed 1 Aug 2012:

Thanks for copying that. I’m not sure how to check whether
both blowers are working. I did run through the tests and
it only works properly in defrost mode. Air comes out of
the demist vents all the time and never from the center
vents. So am I pulling this dash to fix this and if so, is
there a list of parts replace while I have it out so I
don’t have to do it again soon?

Thanks again.–
dtrain
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In reply to a message from dtrain sent Wed 1 Aug 2012:

Judging from personal experience with this issue, I totally
aggree with BryanN on this. When the RH side blower goes
out, the air from the LH will just blow across the dash to
the right side and barely come out the vents. I replaced my
RH blower motor and all the relays and it went out again a
year later. There are so many contacts and relays that one
failure is much more likely. And it’s a pain to stand on
your head for two hours to R/R.

I also had the same prob with the vent flap actuators
breaking. You can buy a factory full service kit that
upgrades the levers and seals. I think I got a good deal on
it from Engel Imports in Kalamazoo.–
Marc , BSME – 93/94 XJ12
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In reply to a message from dtrain sent Wed 1 Aug 2012:

Checking blower operation is quite straightforward.

On your '92 model, turn the fan speed to ‘High’ and observe
the blower noise level. Pull fuse A2 in the right fuse box.
If it goes silent, the LH blower is not working (because you
have just switched off the RH blower which was working).

Conversely,if the noise level doesn’t change then the RH
blower is not working. You can confirm that after replacing
fuse A2, by pulling fuse B1 in the right fuse box. If it now
goes silent (having killed the LH blower) the RH is
confirmed as the one that is not working.

BTW, before ripping out the dash, since neither the centre
vents which require vacuum to open and the demist vents
which require vacuum to close appear to be working as they
should, are you sure you have manifold vacuum going to the
vacuum reservoir under the battery and if so, you need to
check the individual vacuum feeds from the solenoid valves
under the base of the climate control unit (CCU) and the
vacuum lines to those vents.

The centre vents have a black vacuum line and the demist
vents have a green vacuum line from their respective
solenoid valves both of which are on the right underside of
the CCU (demist nearest the firewall, centre vents furthest
from the firewall)

You can remove the vacuum line from its solenoid valve and
apply a vacuum to the line manually (Mityvac or similar) to
listen to the operation of the flaps as vacuum is applied or
removed.–
The original message included these comments:

Thanks for copying that. I’m not sure how to check whether
both blowers are working. I did run through the tests and
it only works properly in defrost mode. Air comes out of
the demist vents all the time and never from the center
vents. So am I pulling this dash to fix this and if so, is
there a list of parts replace while I have it out so I
don’t have to do it again soon?
Thanks again.


Bryan N, '91 Sovereign 4.0 L, RHD
Cambridgeshire, United Kingdom
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In reply to a message from doublesix40 sent Wed 1 Aug 2012:

It is not just a mental frustration replacing the fans it is
a physical pain. Two years ago I replaced my left side and
now the same side is not working 100% of the time. I didn’t
replace the speed control transistor so now I sometimes get
high speed sometimes not.

And I thought the half hour to replace the AC/heat relay on
an SIII was hard to change. It doesn’t come close to the
XJ40 fan box relay nightmare.

I’ve been doing some searching and the AC system is high on
the list of why people sell the car. I swear they were on
drugs when they designed the system.

I’m thinking I really need a second car and remove the Jag

I hope that it is just the center vent that you need to prop
open and not the fan cages.from my DD. As a DD it isn’t working well for me anymore. :frowning:

The original message included these comments:

upgrades the levers and seals. I think I got a good deal on
it from Engel Imports in Kalamazoo.


John 90 XJ40
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In reply to a message from John S sent Thu 2 Aug 2012:

Checked the blowers via the fuses and fortunately both of them
work.

Checked the vacuum lines under the battery tray and they are
good. I will need the weekend to tackle the other lines behind
the climate control.

Thanks for the input - you guys have been very helpful.

I have to agree with you about being on drugs when they put
this system together…–
dtrain
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In reply to a message from dtrain sent Fri 3 Aug 2012:

Once you remove the center vent you can peer at the very
rear of the vent opening. On each side you will see vac
connections for the defrost flaps. Check to see if they are
connected because they could produce some issues.

If they are not connected you can reconnect them but you
will need to find some special tools. Those special tools
are two hemostats, each about 10 inches or longer. I bought
mine at harbor freight. Once you have the tools you get the
fun part of playing surgeon with the hemostats. You hold
the line with one hemostat, hold the ‘‘L’’ shaped vac
connector with the other hemostat and then using your new
found skill, you can insert the line into the ‘‘L’’ connector.

I bet you never thought owning a Jaguar would hone your
surgeon skills.–
The original message included these comments:

Checked the vacuum lines under the battery tray and they are
good. I will need the weekend to tackle the other lines behind
the climate control.


John 90 XJ40
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1 Like

Hello everyone,

Sorry to bump the topic up the list, it seems it’s not a very popular one.:face_with_raised_eyebrow:

I recently bought a 1991 Daimler XJ40 which I love. I always wanted one of theses and I am now the proud owner of this beautiful exemplar.

It seems I have a similar issue than Brian (?)
Both my blowers works, I’ve check by removing both fuses.

I do not have any (or very little) air coming from the defrost vent and none from any other vent. I have a video showing what happens when I operate the knob of the ventilation. https://youtu.be/DCfiscGT3Zg

If anyone has any idea or advise as to what should I try first (and second), that would be very much appreciated.

Link to the video: https://youtu.be/DCfiscGT3Zg

Thanks a lot.