Hello all, after quite a bit of searching I found some threads addressing similar problems but missing some key info. Hopefully I can turn to y'all for some advice.

First off a little info on the cat. It's an 85 XJ6. Ok, on to the issue(s).

It's had excellent heat from the time I bought it. I've rotated the knob and listened for the "whirring" sound as I've read from multiple posts. It does not exhibit any sounds at all, and acts like it is not sending signal. However all fanspeeds work including vents that will change to defrost.

I've taken the kick panel off and cleaned the contacts of all the connectors, Nothing changed. Replaced the vacuum line running from the heater valve to the fender (which btw does not feel like it has vacuum.) Does the metal source on the fender supply constant vacuum or is it sent signal to initiate vacuum from the temp knob.

What I'm thinking it is and this is solely based off searching posts... is the amplifier has gone kaput. I've found multiple posts of cold AC air only and no heat, but none of heat only. I'm assuming it's similar? Also, while I was in the kick panel I noticed two electrical connectors and a harness not plugged into anything and no other obvious open connectors. I'm thinking this could be part of the problem. Thank you.

 

The unused connectors are common; probably not related.

First check all 4 system fuses. One is shown in your picture...the amplifier fuse in the white holder. Two more are in the RH fuse panel below the glove box. One more, another inline type, is clipped to the heater case behind the console RH cheek panel. At least one or two of the fuses must be good since your blowers work....but I can't remember which fuses do what, off hand. "checking fuses' on these cars doesn't mean just checking if they're blown. it also means making sure the end caps are corrosion-free and the clippy things are snug

Cheers
DD

 

Perfect, I didn't know there were fuses on the other side as well. Good to know. I may just replace the fuses all around. It's tough to tell what amp they are. Could you shed some info. Thank you for the quick reply. Your knowledge is amazing on these cars.

 

Those 2 connector are pig tails for the water temp sensor. If you connect them the fan and HVAC system should activate regardless of engine water temp. Jag probably assembled these car in a cold factory and may have engineered in a quick way to test the system.

 

If you still have any of 'em left the original fuses have paper tags showing the amp rating, and the fuse box cover will show the ratings as well

Anyhow....

#16 fuse 50 amp
#6 fuse 35 amp
Amp fuse 3 amp
Fuse on RH heater case 10 amp

But....wait. there's more.

Those are the British fuse ratings. Here's the USA the conversion:

British >>>>> USA

50 amp 30 amp
35 >>> 25
30 >>> 20
25 >>> 15
20 >>> 10
10 >>> 7.5
5 >>> 3

One is constant rating, the others is ....something else. I can't remember the details at the moment

And thanks for the compliment!

Cheers
DD

 

Constant rating is what amps it is designed to pass, the other value is the current to blow the fuse. At least that is my understanding.

 

Update... checked fuses and all looked good. I cleaned the terminals and fuses themselves with contact cleaner.

Question for y'all. Would a faulty "stuck" heater valve cause a constant heat issue? Mine looks original and also looks to not be functioning. I had someone adjust the temp control knob and nothing happened. Again, though I question the system's vacuum. There is none at the fender and none when I pull the line from the valve. So, I'm not sure if that's attributing to the issue or not?

Thanks for your help on this.

 

OK, good. When you turn the temp control knob are you hearing the 'whir'?

Yes.

But there may be more to the story



The heater valve is prone to sticking or breaking. Sometimes they can be coaxed back into operation by manually exercising the actuator arm. Sometimes not.

However.....

The system is designed to refrigerate all incoming air first and then heat it as needed. Thus it is normal for the valve to be open in all modes of operation except when maximum cooling is asked for. When max cooling is called up on the dial vacuum is applied to the valve to close it. At all other times the vacuum is released and the valve opens.

This application/release of vacuum is via vacuum switches that are controlled by the servo. It's the servo that makes the whir noise.

Besides the vacuum hose to the heater valve you have a vacuum supply hose, located in the same neck o' the woods, identified by a white/black check valve. This *should* have vacuum when the engine is running and even a bit leftover after the engine is turned off....thanks to a reservoir tucked into the fender near the brake booster (on a LHD car). If you don't have this supply vacuum you'll need to find out why. Broken hose, most likely.

If you don't hear the whir you'll need to fix that as well !

Cheers
DD

 

No "whir" noise that I can make out. Is it pretty noticeable? That might be why the valve never moves. It's not receiving the all cool signal. What's the best way to manually exercising the actuator arm without breaking or damaging it? I've tried a little bit. Just didn't want to mess it up.

 

Is subtle....but should be no problem when you're intentionally listening for it



Right.



Just use your fingers. Moderate finger pressure will move the actuator arm unless it has seized. Try some aerosol penetrating oil in hopes it can get into the right places...but knowing that the actual valve innards might be stuck fast or physically broken

Cheers
DD

 

I'm pretty positive the temp control knob isn't doing anything or "whiring". I've listened for it deliberately. It also doesn't seem like the AC Amplifier is "talking" to the other parts of the system. Not sure if those two are connected?

I know portions of it work (Compressor clicks when I turn the blowers on low and all the way through Defrost. So at the very least that is working (baby steps) ha.

Back to the whiring (or not) in my case. What part needs to be checked and replaced? Is it fairly easy to access it? Thank you again for your help Doug

 

Yes, they're connected.

The amplifier is the brain of the system. It takes in the signals from the temp control knob and the temp sensors and decides what to do. It commands the servo. The servo is the workhorse of the system...operating all the flaps, vacuum valves, and blower speed switches. It's a little motor that operates a gear driven camshaft....thus the whir



Good !


Most likely the amplifier is kaput. Common fault. Servo failures are rare.

However the servo can be unplugged and tested to verify that it does indeed work. If you wanna do that, post back.

Oh....one other very easy check.......

With the console LH 'cheek panel' removed you can see the heater core pipes. One of the pipes has a small switch attached. it has two wires. Jump the two wires together and see if anything changes.

Cheers
DD

 

Better yet, let's use the info we just learned from ICS !

Don't disconnect the wires at the switch. Jaguar gave us test leads which can be jumped together, as seen in your pictures, to accomplish the same thing. They're the brown and brown/yellow wires with the vacant grey connectors.

Cheers
DD

 

I just love this.

I never noticed or realized this before, despite that fact that the diagrams clearly show the existence of these test wires. [hand hitting forehead]

There's always something new to learn, isn't there?

Cheers and thanks
DD

 

Yes sir, and for you to learn it on these cars still says A-lot! Ha Well, I tried jumping the two leads. Nothing changed. Still no "whiring" which I thought was odd since I'm basically bypassing the amplifier right?

Also not having any luck freeing up the valve. I've let penetrating oil sit overnight. It feel like it's seized up. I just can't get any movement out of it.