[xj40] No Heat

XJ40
1

This is my first posting and my first Jaguar I have a 1991 Baseline
model. I can’t figure out why the heater does not get the car warm
or hot. The vents are working and the engine warms to the center
line, no problems with the A/C. Also the brake light stays on with
VCM message ‘‘Fluid’’ and ‘‘Fail’’ not sure about this, because rotors
and pads are pretty new? Any tips or advice would be great
considering I’m in Minnesota the heat is a concern.–
jsavesus
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2

In reply to a message from Omarro sent Wed 5 Jan 2005:

On your '91 (assuming that the spec is similar to my UK version),
they did not fit the coolant cut-off valve to the heater matrix
which is designed to shut off the coolant flow whenever Aircon is
selected - so it can’t be that that is stuck closed.

Having got that possibility out of the way, have you checked that
you actually have coolant flow through the heater matrix in the
climate control unit (CCU)? When the engine is up to normal
operating temperature, feel the heater pipes that pass through the
left side of the firewall in the engine bay - both should be hot.
If they are not, suspect that the heater matrix is blocked and
remove both pipes to flush it through with water in an attempt to
clear the blockage.

If that is OK, select ‘manual’ mode on the A/C panel and ‘Defrost’
on the fan speed control. Check if a) you get air out of the demist
vents under the screen, b) that the air is HOT and c) that you get
NO air from the footwell vents.

If you get air out of the footwell vents in ‘Defrost’ the lower
blend flap is stuck and if that air is COLD, it’s stuck in
the ‘Full Cold’ position.

If the air from the demist vents is cold when ‘Defrost’ is
selected, the upper blend flap in the CCU is stuck in the ‘Full
Cool’ position.

Try those things first and report back when we may be able to give
you further advice.

On the question of the ‘Brake’ warning of ‘Fail’ and ‘Fluid’ -
check the level of the brake fluid in the reservoir - it’s telling
you that it’s low.

Turn on the ignition without starting the engine. Wait until the
Teves brake booster electric pump stops running. do you still have
the brake warning light on? Turn off the ignition. How many
applications of the brake can you make before the brake pedal ‘goes
hard’ (i.e. all servo assistance is lost.

Report back with that too.–
The original message included these comments:

This is my first posting and my first Jaguar I have a 1991 Baseline
model. I can’t figure out why the heater does not get the car warm
or hot. The vents are working and the engine warms to the center
line, no problems with the A/C. Also the brake light stays on with
VCM message ‘‘Fluid’’ and ‘‘Fail’’ not sure about this, because rotors
and pads are pretty new? Any tips or advice would be great
considering I’m in Minnesota the heat is a concern.

–
Bryan N ('91 Sovereign 4.0 L)
Cambridge, United Kingdom
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3

In reply to a message from Bryan N sent Wed 5 Jan 2005:

Hello Bryan, Thanks for the info I still need to check the heater
pipes that pass thorugh the fire wall, for warmth. I felt the hoses
but was a little unsure of which pipes you were referring to? I
followed your other suggestions and I did get warm air not(hot)air
from the demist vents with nothing coming from the footwell vents.
Once I get the cap off the brake reservoir, I will verify the
levels for some reason the cap is extremly tight? The brake warning
light stayed on after the electric pump stopped running. I counted
about 16-18 pumps before the pedal got hard.–
jsavesus
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4

In reply to a message from Omarro sent Fri 7 Jan 2005:

The two heater pipes pass through the firewall on the left side
just below the windshield wiper motor. One hose comes across from
the back of the cylinder head, the other from the front of the
engine runs parallel with the inlet manifold The hoses are about �’’
diameter IIRC.

It certainly sounds as if you may have a stuck upper blend flap.
With the A/C panel controls set at ‘Manual’ , the fan speed set
at ‘Medium’, the engine at normal operating temperature, turn the
temp control knob to ‘Max Cold’. After a few seconds (say 30 / 45)
are you getting ice cold air out of the centre fascia vents and
cold air out of the side fascia vents? When you then turn the
temperature control knob to ‘Max Heat’, after 45 seconds or so, are
the centre fascia vents closed (negligeable air flow) and do you
now get hot air out of the side fascia vents?

If not, you can be pretty certain that the upper blend flap is not
responding to signals from the ECU. Sometimes you can ‘un-stick’ a
blend flap by reaching up from below (back-breaking stuff!) and,
whilst switching the temp control between ‘Full Hot’ and ‘Full
Cold’, striking the motor body with a blunt instrument - like a
metal rod. The motor is high up under the dash behind the centre
console (I’ll try sending you a diagram off-list to show the
location) on the right side of the climate control unit and I
believe on LHD cars, there is a removable panel in the inboard side
of the glove box which allows access to that motor.

When you have the brake warning light showing, press the VCM
button. Does it still show ‘Fail’ ‘Fluid’? You should be able to
see the brake fluid level through the white / translucent brake
fluid reservoir on top of the master cylinder. There is a line
embossed on the side of the reservoir to show the correct level.

16 to 18 pumps is not the best, but let’s get the other thing
sorted out first.–
The original message included these comments:

pipes that pass thorugh the fire wall, for warmth. I felt the hoses
but was a little unsure of which pipes you were referring to? I
followed your other suggestions and I did get warm air not(hot)air
from the demist vents with nothing coming from the footwell vents.
Once I get the cap off the brake reservoir, I will verify the
levels for some reason the cap is extremly tight? The brake warning
light stayed on after the electric pump stopped running. I counted
about 16-18 pumps before the pedal got hard.

–
Bryan N ('91 Sovereign 4.0 L)
Cambridge, United Kingdom
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5

In reply to a message from Bryan N sent Fri 7 Jan 2005:

That’s right - this is the only use I have ever discovered for that
access door in the glove box.

It does help to know where the blend flap motor is; I think Haynes
has some pictures, as you cannot see the motor from the trap door,
but can only feel it up against the air box.

I open the trap door in the glove box, clear the vacuum lines,
etc., out of the way, and use an offset box wrench to rap the
upper blend flap.

Beats the heck out of taking the dash apart, dropping the relay
rack, etc.

Win Dooley
Fort Smith, Arkansas

90 VDP
1993 Xj12–
The original message included these comments:

location) on the right side of the climate control unit and I
believe on LHD cars, there is a removable panel in the inboard side
of the glove box which allows access to that motor.

–
Win Dooley
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6

I’ve fixed my low fuel pressure bogging issue. Thank goodness.
However � less critical but still important - I have no heat now.
The blowers are going, but it�s obvious that something�s not
getting opened or shut (by a solenoid I assume � or other little
motor) to redirect the airflow over the heater core � or maybe the
heater core isn�t getting hot water � because of some other stuck
valve or such.

If I turn on the AC full, I get loads of air through the vents.
Buth when I switch it to heat or defrost, I hear some movement, and
the air flow to the vents stops, but the blowers are still blowing
hard. If I put the fan speed to low, I get some heat trickling out
of the outer vents, but very very little, and never any through the
windscreen defog vents.

What can I check myself to try & diagnose & fix this new issue �
before I have to burden the repair shop with it again?–
WCManess - 1991 XJ40/6 - Black/Grey - 4.0 liter
Arlington/Texas, United States
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7

In reply to a message from wcmaness sent Mon 9 Dec 2013:

Commonly, the '91 did not come with a water shut off valve
but if it did (or retrofitted), it’d be at the very back of
the cylinder head, under the intake manifold or just peeking
out from under the manifold.

That valve (if installed) might have gotten stuck shut and
is preventing hot coolant from getting to the heater matrix.

2nd thing to check is the supply and return lines to the
matrix. Are they both hot to the touch with the engine at
normal operating temp? If so, you’re getting flow through
the matrix and you’ve likely got a blend flap problem.

If not, the matrix is plugged and you’re looking at
replacing it. (No where near has hard as it sounds)

Bryan has published a great set of diagnostics on checking
the blend flaps, a bit of searching in the archives for
threads about heat issues should turn up the diags in short
order.

Often a sharp rap with a screw driver handle to the blend
flap motor is all that’s needed, it’s getting to those
motors that takes a (minor) bit of effort.–
02 VDP – Driveway’s got too many SAABs in it!
Tampa Fl, United States
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8

In reply to a message from wcmaness sent Mon 9 Dec 2013:

Wes,

Your '91 probably (if the same as UK cars of that era) does
not have the coolant/heater shut-off valve in the line from
the back of the cylinder head to the heater matrix in the
Climate Control Unit (CCU).

You could have a blocked coolant feed to the heater matrix
in that line and to check that you would need to pull the
feed and return lines to the CCU at the firewall and using a
low pressure hose flush out any crap in the tubes.
When the engine is up to normal operating temperature, with
your hands feel those feed and return hoses as they enter
and exit the firewall on the top left corner of the engine
bay. If only one of them is warm, then you have no flow
through the heater matrix.

More likely is that your blend flaps in the CCU are stuck in
the ‘Full Cold’ position so that none of the incoming air is
being directed through the heater matrix particularly if,
when you select ‘Defrost’, you do not get high volumes of
hot air out of the demist vents under the windshield.

Let us know what you find and we can give you more
information on how to check / free those blend flaps
(although it is widely covered in the archives too).–
The original message included these comments:

However � less critical but still important - I have no heat now.
If I turn on the AC full, I get loads of air through the vents.
Buth when I switch it to heat or defrost, I hear some movement, and
the air flow to the vents stops, but the blowers are still blowing
hard. If I put the fan speed to low, I get some heat trickling out
of the outer vents, but very very little, and never any through the
windscreen defog vents.
What can I check myself to try & diagnose & fix this new issue �
before I have to burden the repair shop with it again?

–
Bryan N, now Jag-less, but fun while it lasted.
Cambridgeshire, United Kingdom
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9

In reply to a message from Bryan N sent Mon 9 Dec 2013:

I would vote for the blend flaps. In 13 years I probably
had to un-stick those flaps three times to get heat.

I would release the attachment screws just a bit, spray some
release agent like WD40 into the crack, tap tap tap with the
handle of a screwdriver and everything was good.

I also did have to flush the heater matrix one time and that
made a great difference in the amount of heat I was getting.

I used hot water off the house water heater to flush it.–
The original message included these comments:

You could have a blocked coolant feed to the heater matrix
in that line and to check that you would need to pull the
When the engine is up to normal operating temperature, with
your hands feel those feed and return hoses as they enter

–
John 90 XJ40
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10

In reply to a message from John S sent Mon 9 Dec 2013:

Hmm might have a similar problem.

When I have the fan at position one, I have a nice trickle
of heat, when I put the fan on high the airflow gets
lukewarm, almost cool. We have now about zero, +/- 4 degrees
here so still no panic, but it will get cooler. Defrost air
flow is also weak.
One problem with flushing the heater matrix is that I have
filled Evans coolant (Due to water tank(s) leaking and
squirting out standard coolant, 1-2 liter on a 100 km trip.
Now a very small leak, haven’t have to top up the Evans)

Another thing, the windshield heating works on the right
side only, separate fuses (I hope) or broken circuitry??

Best regards

Ragnar
93 v12
Lund, Sweden–
The original message included these comments:

I also did have to flush the heater matrix one time and that

–
Ragnar Carst
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11

In reply to a message from Ragnar Carst sent Mon 9 Dec 2013:

I was having the same issue with no heat in my 89, and I was
preparing to remove the glove box and play with the blend
cylinder (not really a flap) motors. But I happened to
select ‘‘Auto’’ instead of ‘‘Manual’’ and the system woke up and
delivered a nice flow of warm air from the vents.
Last summer, I took the center facia grille off and propped
the flap open with a short piece of wood. The idea being
that I can easily reach up and adjust the two thumb wheels
to control air from the center vents. And to monitor the
system better, I stuck a small dial thermometer in one of
the grille openings.
I was having issues this summer with the air conditioning.
It would come on like gangbusters, then slowly get warmer
over 20 minutes or so. I took the glove box out to see
whether there were wires disconnected and I found that all
three wires to the outside temperature sensor were broken.
The sensor is attached to the recirculation flap on the
right side blower housing and the wires fatigued and broke
as the flap opened and closed over the years. Of course,
the break occurred between the connector and the harness, so
I had to repair the wires in place. I’ve had the same
broken wire issue on all three XJ40s (two 88s and an 89) so
you may want to inspect those wires when you get the chance.
If you take the center grille out, you can reach in and feel
where the upper blend cylinder is positioned. The cylinder
only rotates about 90 degrees, and it it’s rolled back near
the firewall, it’s in the heat position. If it’s rolled to
near the facia, it’s in full cool position. It will
modulate to maintain a set temperature. But the climate
control computer will get confused if the outside or inside
temperature sensors aren’t connected properly.–
The original message included these comments:

Hmm might have a similar problem.
When I have the fan at position one, I have a nice trickle
of heat, when I put the fan on high the airflow gets
lukewarm, almost cool. We have now about zero, +/- 4 degrees
here so still no panic, but it will get cooler. Defrost air
flow is also weak.

–
Pete Peterson 70E(193K) XJ40s(88-270K,89-97K, 94-122K)
Severna Park, Maryland, United States
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12

In reply to a message from John S sent Mon 9 Dec 2013:

I do not have the water valve on this car - though I’ve been
tempted to retrofit one in the summer many times. I’ll give the
flap smack option a try - after I run through the diagnostic steps
posted in the archives. Thanks - I’ll let you know what the
results are.–
The original message included these comments:

I would vote for the blend flaps. In 13 years I probably
had to un-stick those flaps three times to get heat.

–
WCManess - 1991 XJ40/6 - Black/Grey - 4.0 liter
Arlington/Texas, United States
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13

In reply to a message from wcmaness sent Tue 10 Dec 2013:

Hi,
I’ve experienced a sudden loss of warm air from the heater
twice now, once in my old 4.0l Sovereign and also with my
current car. On both occasions it was the engine coolant
thermostat stuck wide open. Even on a long drive the air
from the heater would be only barely warm.
Also, although the temperature gauge on the dash did read
slightly lower than usual each time, it was not by much and
could go unnoticed on a short journey.

good luck.–
Casso - 1993 Jaguarsport XJR 4.0 A.
Liverpool, United Kingdom
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14

In reply to a message from wcmaness sent Mon 9 Dec 2013:

I’m fighting the same issue with my 89 in the snows of
Maryland. I removed the glove box (8 screws and 2 bolts)
and the driver’s knee bolster for better access to
components. Both blowers are running. Both heater pipes
will burn my fingers. Both flap actuators are turning, both
flaps are free and can be easily turned with a flat-blade
screwdriver. It appears both are in the correct position
for heat. When I rotate the upper flap to the A/C position,
I get lots of air from the center vent, but none when I
rotate it to the heat position. I took the heater matrix
cover off on the right side, and get a good blast of air –
I can see a bit of the A/C matrix and it looks clean. The
end cap of the heater matrix is hot to the touch. I think
the heater matrix is fouled on the air side.
My next step is to remove the instrument cluster for better
access (4 screws hold it in), then clamp the heater hoses in
the engine compartment, then pull the heater matrix.
I’ll let you know what I find.–
The original message included these comments:

However � less critical but still important - I have no heat now.
The blowers are going, but it�s obvious that something�s not
getting opened or shut (by a solenoid I assume � or other little
motor) to redirect the airflow over the heater core � or maybe the
heater core isn�t getting hot water � because of some other stuck
valve or such.
If I turn on the AC full, I get loads of air through the vents.
Buth when I switch it to heat or defrost, I hear some movement, and
the air flow to the vents stops, but the blowers are still blowing
hard. If I put the fan speed to low, I get some heat trickling out
of the outer vents, but very very little, and never any through the

–
Pete Peterson 70E(193K) XJ40s(88-270K,89-97K, 94-122K)
Severna Park, Maryland, United States
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15

In reply to a message from Jaguarpete sent Thu 12 Dec 2013:

Pete,

When I pulled the dash on our '93 to repair the demist flaps
and tweeters, I found that virtually all of the original
rubber foam insulating seals had deteriorated and fallen
into the ‘‘V’’ valley between the core & evap and nearly
half-filled that valley. I also found lots of foam crumbs
on the back side of the ‘‘V’’ which I couldn’t completely get
to with the assembly in situ, but there is a passage behind
the V due to the angle at which it is mounted and I cleaned
that with a smaller hose attached to my shop vac. I’ll be
very curious to hear what you find.

Don–
The original message included these comments:

I get lots of air from the center vent, but none when I
rotate it to the heat position. I took the heater matrix
cover off on the right side, and get a good blast of air –
I can see a bit of the A/C matrix and it looks clean. The
end cap of the heater matrix is hot to the touch. I think
the heater matrix is fouled on the air side.
My next step is to remove the instrument cluster for better
access (4 screws hold it in), then clamp the heater hoses in
the engine compartment, then pull the heater matrix.
I’ll let you know what I find.

–
Don B : '04 XJR '93 XJ40 VDP ex-'88 XJ40 Sovereign
Franklin, TN, United States
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16

In reply to a message from Don B sent Thu 12 Dec 2013:

I pulled the heater core and flushed both air- and
water-sides and vacuumed loose foam from where ever I could
reach in the housing. Put it all back together and still no
heat and very, very little air from the vents when on heat.
I decided to replace the thermostat – AutoZone has them
for $16 with a warranty, mind you – so it was pretty easy
to replace it. The old thermostat seemed to operate as it
should (although it was stamped 87C, I think it was opening
early) Now heat oozes out of the vents but there’s not much
wind at all. But SWMBO seems to be pleased, so ripping the
unit apart can wait until warmer climes. Thanks all for the
suggestions.–
The original message included these comments:

When I pulled the dash on our '93 to repair the demist flaps
and tweeters, I found that virtually all of the original
rubber foam insulating seals had deteriorated and fallen
into the ‘‘V’’ valley between the core & evap and nearly
half-filled that valley. I also found lots of foam crumbs
on the back side of the ‘‘V’’ which I couldn’t completely get
to with the assembly in situ, but there is a passage behind
the V due to the angle at which it is mounted and I cleaned
that with a smaller hose attached to my shop vac. I’ll be
very curious to hear what you find.

–
Pete Peterson 70E(193K) XJ40s(88-270K,89-97K, 94-122K)
Severna Park, Maryland, United States
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17

Hi Pete.
Do the blowers sound as though they are working hard?

From your description I would surmise that one of the blowers has gone to
sleep.
Have you tried pulling the relevant fuse from each side of the car to
determine if that is the problem?
Regards Robin O’Connor
'92 XJ40 4.0 Ltr
'66 'S’Type MoD
'95 XJ6 4.2 LWB
Auckland NZ----- Original Message -----
From: “Jaguarpete” jaguarpete@aol.com
To: xj40@jag-lovers.org
Sent: Friday, December 20, 2013 4:23 PM
Subject: Re: [xj40] No Heat

In reply to a message from Don B sent Thu 12 Dec 2013:

I pulled the heater core and flushed both air- and
water-sides and vacuumed loose foam from where ever I could
reach in the housing. Put it all back together and still no
heat and very, very little air from the vents when on heat.
I decided to replace the thermostat – AutoZone has them
for $16 with a warranty, mind you – so it was pretty easy
to replace it. The old thermostat seemed to operate as it
should (although it was stamped 87C, I think it was opening
early) Now heat oozes out of the vents but there’s not much
wind at all. But SWMBO seems to be pleased, so ripping the
unit apart can wait until warmer climes. Thanks all for the
suggestions.

The original message included these comments:

When I pulled the dash on our '93 to repair the demist flaps
and tweeters, I found that virtually all of the original
rubber foam insulating seals had deteriorated and fallen
into the ‘‘V’’ valley between the core & evap and nearly
half-filled that valley. I also found lots of foam crumbs
on the back side of the ‘‘V’’ which I couldn’t completely get
to with the assembly in situ, but there is a passage behind
the V due to the angle at which it is mounted and I cleaned
that with a smaller hose attached to my shop vac. I’ll be
very curious to hear what you find.

–
Pete Peterson 70E(193K) XJ40s(88-270K,89-97K, 94-122K)
Severna Park, Maryland, United States
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services and resources including Photo Albums, Event Diary / Calendar, On
Line Books and more !

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18

In reply to a message from Robin and Maureen O’Connor sent Thu 19 Dec 2013:

I’ve verified both blowers are running by pulling fuses.
There’s a great roar coming from the blowers, and it’s
enough to ruffle your hair on A/C, but just a whisper of air
from the vents on heat. I’ve already blocked open the
center vent flapper.–
The original message included these comments:

Do the blowers sound as though they are working hard?

From your description I would surmise that one of the blowers has gone to
sleep.
Have you tried pulling the relevant fuse from each side of the car to
determine if that is the problem?

–
Pete Peterson 70E(193K) XJ40s(88-270K,89-97K, 94-122K)
Severna Park, Maryland, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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19

In reply to a message from Jaguarpete sent Fri 20 Dec 2013:

Pete,

Deep breath!..

If you are convinced that you are getting hot coolant
through the heater core in the CCU but the problem is that
you are not getting airflow through the heater core and out
of the upper and lower exits of the CCU despite the fact
that both blowers are pushing air in to the CCU, one must
assume that the problem is something to do with the upper
and lower blend flaps in the CCU.

Now it is easy to imagine how the lower blend flap could
prevent air leaving the lower exit from the CCU towards the
foot-wells because that is exactly what it does when
‘Defrost’ is selected.
However, it is more difficult to see how the upper blend
flap can close off the upper exit from the CCU towards the
fascia vents and demist vents because it normally only
rotates through about 90� between full hot and full cold and
in either position or at any blend angle in between, the
upper exit to the CCU is never entirely blocked by that flap.

Is it possible that somehow your blend flaps are ‘out of
sync’ so that when you select heat, the lower flap rotates
in to the ‘Defrost’ position (thus blocking off the lower
exit from the CCU) and the upper flap ‘overrides its stops’
by a further 90� from the ‘full heat’ position so that it
blocks the upper exit from the CCU?

Is it possible for the blend flap motor/gearbox units or the
blend flap feed-back potentiometers to be fitted ‘out of
kilter’ on the the flap shafts?–
The original message included these comments:

I’ve verified both blowers are running by pulling fuses.
There’s a great roar coming from the blowers, and it’s
enough to ruffle your hair on A/C, but just a whisper of air
from the vents on heat. I’ve already blocked open the
center vent flapper.

–
Bryan N, now Jag-less, but fun while it lasted.
Cambridgeshire, United Kingdom
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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20

In reply to a message from Bryan N sent Fri 20 Dec 2013:

Bryan:
I checked all of that when I had the heater core out
last week. At the time, I verified that the potentiometers
were in their correct positions (there are alignment pins in
the plastic box that position the potentiometer plates, and
they’re there). The gear motors are small permanent-magnet
motors that drive a 1,500:1 ratio worm-and-spur-gear train,
so they have sufficient torque to overcome drag of the
rotary valve (blend flap) edge seals. I surmise that the
gear motor/potentiometer correctly positions the rotary
valve for function required. I do know that the gear motors
drive in both directions when moving from heat to cool with
the motors dismounted. The potentiometers are driven by the
rotary valve via a blade-in-slot coupling. I did not check
to see whether they could be installed with that connection
180 degrees out It appears that the rotary valves can be
removed when the potentiometer plates are dismounted, and I
will probably do that after the holidays. Access is
actually very good with the instrument cluster removed (just
four 8 mm bolts hold it in).
But for now, the cabin warms nicely and SWMBO is
satisfied (or, at least, not unhappy). On to other issues.–
The original message included these comments:

If you are convinced that you are getting hot coolant
through the heater core in the CCU but the problem is that
you are not getting airflow through the heater core and out
of the upper and lower exits of the CCU despite the fact
that both blowers are pushing air in to the CCU, one must
assume that the problem is something to do with the upper
and lower blend flaps in the CCU.
Is it possible for the blend flap motor/gearbox units or the
blend flap feed-back potentiometers to be fitted ‘out of
kilter’ on the the flap shafts?

–
Pete Peterson 70E(193K) XJ40s(88-270K,89-97K, 94-122K)
Severna Park, Maryland, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

Visit the Jag Lovers homepage at http://www.jag-lovers.org for exciting services and resources including Photo Albums, Event Diary / Calendar, On Line Books and more !