I was reading the thread for HVAC help and my car is doing that also. I have a hissing sound when I change my controls and also I can hear the flaps move sometimes. I called my local Jag mechanic and he said the valve was probly stuck it barely was I am able to move it now after some Wd40. But when I hook-up or diconnect the vacuum hose it doesnt seem to move at all. My heater seems to work when I first turn it on but then gradually and quickly gets cold. I change my thermostat already Is there two in my car? I called the mechanic here locally and he said there was only one my car also runs just fine tempature wise. The thread also said there was four fuses where are they located.

 

If it is a V12 it has 2 thermostats ( I assume you are referring to engine temp thermostats) and these will have no effect on the heater.

More than likely you have a jammed heater tap (this is the valve the mechanic is more than likely referring to). It is located on the firewall about the centre of the V. It can be difficult to remove patience is required. I replaced mine with one from a local GM vehicle and worked fine. If this is the problem you will need a tap that is normally open and closes with vacuum. This is where I would start, fault finding the HVAC is a process of elimination.

cheers
Warren

DOH just saw your signature.
I should have said operate the temp control. Put HVAC in manual mode and turn full cold the tap should move closed turn full hot and the tap should open, check this operation before you go pulling it out.

 

Is the hissing more like a "whir" ? A whir is normal.

A hiss suggests a vacuum leak.

Quote:

I called my local Jag mechanic and he said the valve was probly stuck it barely was I am able to move it now after some Wd40. But when I hook-up or diconnect the vacuum hose it doesnt seem to move at all.

Sounds like you need a new valve. But....when you removed the hose was there any vacuum?

No vacuum = open heater valve = heat.

Quote:

My heater seems to work when I first turn it on but then gradually and quickly gets cold. I change my thermostat already Is there two in my car? I called the mechanic here locally and he said there was only one my car also runs just fine tempature wise. The thread also said there was four fuses where are they located.

Two thermostats.

Did you bleed the air out of the system after replacing the thermostat? If not you almost certainly have an air lock which could easily cause problems with the heater


Cheers
DD

 

the other guy says the second thermostat wont affect my heater but how will it not is my question the gauge is running about half wat between cold and normal. Can this system be bleed or is it just wait for the air to work its way out

 

the vale is working fine now I have my dash apart and everything seems to be working right but still no heat. I bought a second thermostat to try does it matter which way it sets in there does it have to be opposite the other one for a flow???

 

Your thermostats have absolutely no effect on your heater at all. You are barking up the wrong tree and frankly are likely to cause (or may have already caused) more problems by opening up the cooling system and introducing air. You now need to follow Doug's coolant bleeding instructions to the letter before you do anything else, because you have no way to know if the heater matrix is airbound or not.

If you are going to ask for our help, please take our advice. A previous poster told you your thermostats had nothing to do with it and now you want to go change the other one, without having yet answered our questions: Do you have vacuum to the heater valve line, and are you hearing a whirring noise like an electric motor, or an actual hissing noise like a broken vac hose?

If your heater valve was stuck before, change it. The plastic replacements cost $15 and take ten minutes to replace. As I work through my own car, I'm finding the concept of "difficult" or "a giant pain in the ***" is entirely relative. Just remove your manifold crossover pipe (3 hose clamps) and a 7/16" socket pulls the old heater valve off the firewall. Not that bad. Same with when I changed out my alternator, rear brake calipers, and radiator - everyone says what a nightmare they all are to replace. Not that bad.

Getting the air out of the radiator was a whole 'nother story, though, and a joy that you now get to undertake since you changed a thermostat. Find Doug's instructions and spend the next week performing his bleed procedure once a day to make sure all the air is out. May as well change that heater valve before you bleed.

In the meantime, report back - do you have vacuum to the heater valve, and is it a motor you're hearing or a vacuum leak?

Good luck,
Darel

 

This man speaks the truth... the XJS foibles are well documented.

 

ok i cant find dougs bleeding instructions for the water system. I do have vacuum to the valve and it is working fine i also checked the flaps that i can reach from the inside under dash and they open and close with there vacuum hoses it is actually moving from defrost to heat now when I change the knob.

I put it in auto mode and listened a few times and am not hearing anything at all

I am at your mercy lol its cold out and I need to get this heater going

 

where are he four fuses that doug speaks of I replaced one I found under the dash and now when I turn on the heater the electric fan on the radiator turns on is this a good thing?? Anyone know where the four are he is talking about

 

It can and must be bled. Methods vary slightly. I posted the method I use some tiem ago....I'm sure an archive search will bring it up

Cheers
DD

 

Here's a cut-n-paste on cooling system bleeding from an older posting:




There are different opinions on what works for filling and bleeding. Here's what always works for me. It's not difficult, just messy.

Elevate the front of the car about 8" and then elevate the left front another 2-3" beyond that.

Remove the bleeder plug from the left radiator tank. You'll see an access hole in the radiator upper mounting panel. The plug is some arcane size but you'll find something in your toolbox that fits.

Remove the caps from the expansion/header tank and from the filler pipe at the front of the engine....up there by the A/C compressor.

Add coolant/water to via the filler pipe until it reaches the bottom of the pipe. Start engine, set heater control to max heat. Let it run at idle until it warms up. Peek inside the filler pipe every minute or so and top up as needed.

When the engine gets warm increase the idle to about 1000-1200 rpm (a helper is helpful here...or just wedge a little something in the throttle linakge to hold it sligtly open for a high idle.

Let 'er run and run. Give the upper radiator hoses a few squeezes now and again. Keep checking your coolant level in the filler pipe and top off as needed. Eventually you'll see some coolant coming out of the bleeder. That's good. Wait a while longer and (hopefully) you'll see coolant *really* pouring out of the bleeder. (How much? It's one of those "you'll know it when you see it" things..very messy)

When it's *really* pouring out of the bleeder hole, put the plug back in. Wear some gloves so you don't get scalded. If you can't get the plug back in thru all the gushing, shut off the engine and do it....but I like to leave the engine running if I can. Not worth getting burned, though.

Top off the coolant in the filler pipe...I go right to the top... add a quart or so to the expansion tank, button everything up, and yer off to the races.

 

There should be an inline fuse on the ground wire of the climate control amplifier, which is behind the console left side "cheek panel".

Another inline fuse should be clipped to the RH side of the heater casing...behind the RH cheek panel. Look for brown and yellow wires.

The other two fuse will be in the regualr fuse boxes....probably both in the RH side fuse box but I don't have the manual for your specific car handy.

Even if a fuse isn't blown the end caps might be corroded.

Cheers
DD

 

To clarify "working fine".....

When you select full heat with the temp knob there is NO vacuum at the hose and the heater valve opens.



I think you're operating the recirculation flaps. The flaps that direct air throigh the heater core are inside the heater case



The temp knob?

Let's narrow this down a bit. If you leave the mode control in "auto" and select max heat with the temp knob, does the air flow thru the vents change? With full heat selected air should come thru the footwell outlets. With full cold selected ait should come out of the center dash vent. With a medium temp selected you'll get a blended flow from footweel and R-L dash outlets. Does any of this happen?






So, in "auto" mode you're not hearing a faint whir noise when you adjust the temp knob to a different setting?

If the answer really is "no" then the servo isn't working. The servo controls the flaps...which would direct air thru the heater core. The servo is controlled by the amplifier.


Cheers
DD

 

doug thanks for your help I was in longview on tues. was thinking it be nice to bring car to you lol.

anyway the valve only works when I remove the vacuum line doesnt work with the temp knob. I will check tomorrow on the airflow when I change the temp.
And I cant hear a whir I think i do sometimes but not sure.
I bleed the car water system today thanks for the help on that. Still no hot air though dang it.
The guy that does my mechanics when I cant figure it out thinks he has a hcu that we can hook up and try but he is 75 an hour so Im trying everthing i can figure out first thank you doug and everyone for your input

 

Sounds like your amplifier has failed to full-cold, the same way mine did. You can check to make sure the servo isn't bad by pulling the "cheek panel" by the passenger's side feet and locating a big round electrical connector. It's a 13-pin connector but you're really only using 8 pins. It may be tucked in there a little bit but it will be down near the bottom and close to the front of the console. Pry this apart.

The next part involved fidding with a few jumper wires - if you're not comfortable don't proceed but it's not that bad.

Separate the connector. You are going to be using the half of the connector that goes into the dash closer to the front of the console (not the one that loops back around to the amplifier on the other side). This is where the amplifier feeds the servo.

Find the purple and the red wires that go to this servo. These control the direction the servo rotates - one way for cold, the other way for heat.

You are going to be putting 12v across these two wires - find a good ground to run a jumper from, and a 12v source. If your amp is bad, you might be getting a constant 12v from one of the pins on the OTHER side of the connector you just pulled (the side that loops back over the dash to the amp). If you don't have 12v with the key on at any of those pins you'll have to borrow from the fuse panel.

On the servo connector, running a ground to the purple wire and 12v to the red wire forces the servo to turn to full cool. Reverse the wires (ground to red and 12v to purple) makes it turn to full heat. Try doing this and see if the motor whirs and you can see the two linkage rods under the cheek panel move. If so, your amplifier is bad. You can also just keep letting it rotate until you get heat out of the car (don't let it overtravel, stop when you feel heat) and then just DON'T re-connect that big connector and you will now be locked into heating mode until you can locate a replacement amplifier.

Let us know how it goes.
D

 

Oh, before doing this pull the vac hose off the heater valve and plug. You won't get any heat with the heater valve constantly being forced shut.

 

ok so i tried the wire harness method and the one i found was a 16 point with a red and purple side by side with the ingition on nothing happened either way with the ignition off the blower came on but no movement with the linkages.

However today was a lil bit warmer that the past few and last night i bleed the car to doug style and got alot of air out. on the way to work (45 min) no heat at all. On the way home i had like a luke warm heat was it because it was warmer or did i do some good.

is there any way to move those linkages by hand and get some heat its my wifes car and she refusing to drive it and its a cold ride for me to work. She talking bout selling it but that makes me wanna cry lol. I know a little bout cars but I have had to research everything on this car as jags are like nothing ive ever drove before weve kinda bonded lol

 

I spent half an hour typing a reply and lost it when my wireless cut out, and now my arthritic fingers hurt.

Did you check for voltage on red and purple to ground? Did you try sending 12v to purple and ground to red as described above?

DO NOT force the linkages by hand.

Check the inline fuse on the ground wire of the amplifier too. Driver's side cheek panel, close to the front of the console (close to a second 16-pin connector that goes into the amp).

 

Just to add to Darel's post, I was able to achieve the same effect as jumping the wires from the multipin connector by just unplugging a two wire connector with the purple and red wires that seems to go from the harness to the servo itself. It is very easy and is accessible by removing the passenger side panel with the floor vent in it. I hooked the power and ground up to my passenger interior light wires (my door was open) and activated my servo manually. Alligator clips on a jumper wire did this just fine and I personally found it easier than when I dug out the larger connector. Now I have full heat with no issues but I will have to make a permanent fix come summertime obviously. I hope this helps. The amplifier was my car's problem.

 

I tried checking for power from the red or purple but my tester seems to not be working gotta get a new one. I did try the the power and ground opposite each time and I blew the fuse on the driver side cheeck so. I am going to look and see if the ground inline is broke now . but i never did get any movement on the pushrods