Heater Control Valve

[KeithC]

The heater control valve on my 1990 V12 is suspect. It's the vacuum operated valve mounted on the bulkhead, centre of the engine bay right below the air intake grille.
The symptoms are that it has difficulty switching from cold (air con) to heat and vice versa.
It seems that when cooling is called for a vacuum is applied which closes the hot water valve. By manually applying a vacuum it does seem to operate, but the outlet pipe from the valve still gets, or stays, hot.
Obviously on freezing cold mornings like we have had of late it just blasts out ice cold air but generally speaking I struggle to get cold air from it. The air con system itself has just been overhauled and working fine.
I have purchased a new valve and so my first question is, has anyone replaced one before, and if so, how?? The connections are simply two water pipes and a vacuum pipe which is easy enough, but just how do you remove the b**!!y thing from the bulkhead with out taking the engine out first?
Secondly, anyone know what controls the vacuum, how and where from?
Finally, could the heat control flaps be working incorrectly? I can hear them operating when I switch the fan on/off, but maybe not properly? How easy or otherwise is it to check these?

Apologies for the length of post and number of questions, but I really don't need freezing cold air blasting around in these sub zero temperatures

Cheers
Keith
<edited to correct typos>

[Mark_B]

I've had 2 of these water cutoff valve so far fail, I found they tend to last about 3 years each, they either stick shut, open or take turns between the two. If sticking I found you can get a few more weeks use by dripping some oil onto the twisty-round bit in the middle. It is take-off-able without removing engine, you are in for some scraped knuckles though.

This water valve controlled by an electric vacuum valve behind the radio along with 3 others that working air shutoff flaps located at various points. These 4 soleniod valves under control by the ECU attached to side of the heater unit with about 40 wires connected.

Trick I used in past is remove both blower motor fuses and listen carefully at feint whirring servomotors (2) controlling internal air blend flaps and clicking vacuum valve solenoids in reponse to settings of the temperature control set to manual. There's usually enough vacuum stored in the reservoir to test exercise all the actuators (including the water shutoff one) a couple of times, otherwise need to run the engine a few seconds to refresh.

With temperature knob to manual, coldest setting, the centre vent is open, water valve is shut, air recirc flaps open either side

and rotated very slowly clockwise 90 degrees these things should happen in this kind of order: recirc flaps close, water valve open, centre vent close

[KeithC]

Thanks for your reply Mark. Somehow I just knew it wasn't going to be easy or straightforward. The joys of Jag ownership.

I should have never bought a Jaguar because I have this inbred need that everything in the car must work. Whether I use it or not, it *must* work. Maybe those Morris Minors don't look so bad after all....

But Jaguar are also in my blood so it's sore knuckles and many expletives I suppose

Thanks again mark

Cheers, Keith

[SimonR]

I should have never bought a Jaguar because I have this inbred need that everything in the car must work. Whether I use it or not, it *must* work.

I understand completely! I have this same problem: if Jaguar fitted it to my car then it has got to work, even if it means a lot of expense and skinned knuckles...

Even worse, I've found myself thinking of upgrades to make it an Even Better XJ-S.

It's not healthy, is it?!

[KeithC]

It's far from healthy. I get angry that my left electric mirror will move from side to side but not up and down. It annoys me irrationaly, I mean, after you've adjusted the mirrors once when do you ever need to do so again? But I find myself trying to just in case it's started working again.

Why do I put up with it? It's love. Pure love.

[Telsmoneypit]

Undo the two screws holding the mirror control panel to the door liner and move it away. Carefully pull the wires and connectors through the hole. It's not unknown for the connectors to come adrift resulting in loss of movement with the mirror glass. If you do find these have come apart, connect them up again and hold the lot together with cable ties to prevent this from happening again.

If that doesn't work, have a listen to the mirror as you move the toggle. If there is sound from the motor it's likely that the mirror glass has unattached itself from its ball socket. You need to remove the glass (careful...there is a heating element on the back of the glass) and align the motors so that the glass firmly locks in its sockets.

No sound from the motor? Most probably cream crackered then. I have seen mirror repair kits on ebay that include new motors so thats possibly your best option, otherwise it's new mirror time!

Hope this helps

Terry

[Mark_B]

Theres a guy from the USA that's been trying to sell a pair of xjs mirrors on ebay for the last couple months, keep seeing it readvertised. either that or he's found a bottomless barrel of them. i think he's called antiques or something.

[KeithC]

Thanks for the info guys, sorry it's taken a few days to reply.
The heater valve is now fitted. Yes, sore knuckles and a broken watch, plus many expletives.
But....
But, it all seems to be working hunky dory. And it's bliss to have warm air blowing out. Let's just hope nice cold air blows out in the long hot summer coming up
And I'll try those tips for the mirror.
Thanks again

Keith

[KeithC]

Just for possible interest ....

My old heater comntrol valve appeared to work okay whilst still in the car. By removing the vacuum pipe and applying a vacuum manually the linkage on the valve moved to it's full extent.
However, when I removed the valve from the car I found that with no vacuum the actual valve inside was in the half open position. Applying a vacuum moved it around the proper quarter turn but of course that positioned it half open as well. Or maybe it was half closed then

So, in either position neither the heating, nor the cooling, were working properly.

Bought a new valve from Jaguar at a cost of about 30 quid and all works hunky dory now.

Cheers, Keith