Right, these seem to be two different issues, so let me agree with @fmertz that you should focus on the heat while ignoring the AC compressor/light/clutch for the moment.

I don't believe the AC is the problem. That SEEMS to be working exactly as designed even if we might be smarter and would have designed it a different way

One note: I see my fan come on full speed and then slow down once the car believes it's gotten the cabin to a good temperature. It might take a few minutes. If your AUTO stays on full speed even when temperature is close, that may be a symptom of malfunction.

 

I managed to flush the heater core but it took cutting the hoses at the heater pipes as I could not get them to come off and the heater pipes seem delicate. I will splice replacement hose bits in with some stainless 90 elbows & that should flow better (I did see where it was posted there can be a "kink" in the return bend but the service manual notes this is a factory flattened area in the hose so even though mine did appear kinked at that point I do not think it actually was). There was crud in the core but it was not clogged, lots of flow while flushing it..
I powered up the circulating pump with the hoses off and did not see any liquid coming out, although I do hear the pump running. Looks like I need to remove the pump & see about repairing it. Oh, joy!
If anyone has tips on removing / repairing / replacing the pump & valve I sure do need them.
Next up is accessing the ambient temp sensor and applying some warm air to it while monitoring the EXT TEMP display, and testing the solar sensor...

 

This is the hard part. Is the lack of flow due to a stuck impeller, or a closed valve? Hard to say. The valve defaults open, so unplug it and re-test. The pump can easily be tested by shorting 30 and 87 from the relay location.

 

When I wrote "I powered up the circulating pump" shorting 30 and 87 from the relay location is what I did. I faintly hear the motor spin, but no liquid comes out. Stuck impeller?
I will try it with the valve unplugged.
I found this thread:
https://www.jaguarforums.com/forum/x...w-96841/page2/
very helpful
On the super-charged 4.0 engine, can the pump & valve be accessed with only removing the throttle body (not the super-charger)?

 

This is how I did my pump on my 99 4.0.

Link to heater pump. http://www.jagrepair.com/JaguarXK8HeaterPumpValve.htm

Gus
www.jagrepair.com

 

Ok. I am just a simple guy who looks at things quite simply. If your internal cabin temp sensor thinks the cabin is too hot all the time it will keep pumping out the cold air. Have you tried just swapping the sensor over for another? What would happen if you just disconnected it? Have you tried one of those keyboard cleaning aerosols that will practically freeze the sensor to see if it will switch off the AC? The sensor is easy to get to, just cleaned it myself. https://www.jaguarforum.com/showthre...=1#post1145503

 

Thanks for the link post, Gus. I had not considered going at it from below...
Good suggestion, I think the idea of applying cold air to the cabin temp sensor is interesting, I have been able to confirm the sensor and fan are not dead but as I do not know what resistance at a given temp is correct there is no way for me to determine if it is out of spec. Having to buy a new sensors to find out if mine are out of spec could become an expensive troubleshooting technique
(speaking of which, compiling a sticky of sensor test data would be handy '-)
Can anyone confirm that part # MJA6554AA includes the temp sensor? It is listed as the "housing"... actually this part is not terribly expensive but as I am looking at dealing with the heater valve & pump...
Speaking of which, is there anyone rebuilding the pumps in North America?

 

At this point you've identified the valve and pump as specifically questionable, right? Is there a reason to think those aren't the whole problem?

I didn't see it answered above, but did you try running climate control with the temperature set to HI? I believe that should over overridden all of the sensors anyway and just tried to pump out the heat.

Shooting sensors with aerosols may risk damage to the sensors. I wouldn't do it unless I was sure there was a unexplained problem left to tackle.

 

As for the sensor it is located on the right on a left hand drive car the opening on the left has no sensor.



Before you start ordering anything you need to purchase a stethoscope from you local auto parts place and see if the heater pump is working. With the engine running you can fish the stethoscope down from the top and hear the pump running. If it is not running then check the fuses. As for the solenoid valves that are mounted above the pump they can be reached / R&R from the top but it is no fun but first check power to them.



Have you checked the codes? This should help.

 

Good suggestion. I had forgotten about those. I had a problem a couple of years ago, was able to pin point the problem through the codes.

 

OK, so I am thinking the heater pump issue is a stuck impeller. Bypassing the pump relay I can tell the pump is definitely running, I disconnected the valve wiring connector, put vacuum pump on the heater pump outlet hose, fed a funnel of water to the heater return hose, and got nothing out of the pump. Same with the valve plugged in.
As far as I can tell pulling a vacuum on the heater pump outlet hose I should have got liquid in either valve state (either recirculated heater fluid or engine coolant fluid), so even if the valve is stuck I should have got liquid coming out. The check valve on the heater return is in the correct direction, I have yet to try the ortho-scope to inspect the other check valve but that would not impede flow with the valve closed.
Will a stuck impeller stop all fluid flow?
Has anyone been able to free a stuck impeller with the pump in the car?

ACCM Codes checked early on. Found error 11 & 14, I cleared them and they have not returned.
I have now checked all ACCM sensors (I put crushed ice on the ambient air sensor and watched the "EXT" temp display drop way down, I did the "Volt Meter" test on the Solar Sensor and saw about .5VDC with light and no voltage without, other checks described earlier). NPF.
I do believe the heater issues are a separate, unrelated problem from the AC clutch not cycling off at all no matter where the temp is set.
I can see heat taken into account in the AUTO mode, but not in the AC mode.
As far as I can tell the AC system is designed to function normally (as in NOT requiring heater function)
The ACCM sends a "Clutch On" request to the ECM when the cabin temp is above the set temp, then the ECM sends a LOW state to close the clutch relay. If the relay was faulty it would either never turn on the clutch or it would be on all the time whether in AC, AUTO, or OFF. It is not on in OFF.
There are several systems to keep the clutch from engaging, none to keep it from disengaging.
Does this leave the ACCM as the only possible culprit? (maybe I will try a nice, log battery disconnect!)

 

I went ahead and checked the owner's manual. It says, "The refrigeration system is automatically engaged when 'AUTO' is selected. All year use of air conditioning is recommended for optimum comfort and to reduce interior misting."

That's their bolding. I interpret that as saying yes, the compressor is designed to run regardless of temperature. It's supposed to operate that way because with these cars Jaguar is more interested in driver comfort and defogging than gas mileage or wear on the compressor.

So both AC mode and AUTO mode run the compressor to chill the air, using the heater to get to the right temperature. So what's the difference? AUTO mode also takes over the fan speed and arranges the vents to best circulate air.

I really think you're seeing the correct functioning of that clutch. That's just how these cars are designed to operate.

 

As you can see from the above I did suggest this earlier. However it seems like this is not the problem. I gather he gets icy cold AC no matter how high he turns up the heat and he cannot turn it off? Have I got that right?

 

There is good information about the valve here: xj8-heater-valve-26589

Problem is, with limited access (basically the heater core hoses), being able to come up with a firm diagnostic, knowing that getting to either pump or valve is a bear of a job, and each part so expensive...

Other part is to eliminate all the simple scenarios that do not involve the pump or valve, like dirty heater core, pinched hose, etc.

Also, try and gently beat the pump core and the valve to see if they can be convinced to work again (long screwdriver and a rubber hammer). Try and feed the pump in reverse polarity to see if reversing the rotation gets it unstuck.

Past a certain point, you will have to bring all these parts on the bench for proper testing, unfortunately.

 

Forcing water into the pump in reverse direction is an excellent suggestion. Anything I can do to possibly free the impeller without removing these parts is well worth trying!
Could someone try running their system in AC mode set to a high temp and take a look at the compressor clutch action? Firsthand observation of a properly working system to confirm whether the AC cycles the clutch similar to most other car's systems or stays on constantly regardless of temp setting when in AC mode would be very helpful information.

 

In both AC and AUTO mode my clutch engages with a high temp set.

 

I meant reversing polarity on the electrical feed to the motor to make it spin in reverse. This is a simple DC motor, right?

 

Ah, so, reversing polarity is a good suggestion as well!
I will try both. Maybe at the same time!
Volkris, you write "In both AC and AUTO mode my clutch engages with a high temp set"
Does it stay on constantly or cycle? Even at MAX temp setting? (thanks for checking)
Is there an audible indication of the valve working when testing it by applying +12 VDC ?

 

I don't know if this is the right pump or if it's relevant, but I looked up what I remembered seeing in the XK8 Bible (2003-2006MY):
The service life of Auxiliary Pump is around 100Kmi since it runs anytime ignition is ON, wearing brushes out. Motor case and shaft are also a poor fit and binding of impeller against divider plate can occur. Motor rotation doesn’t mean the magnetically coupled impeller is actually pumping.

If I have time I'll see if the AC cycles off even at HI temperature setting. I can say it does turn on at temperatures well above room temp, but that's just from my experience, and the reason I rarely run it in AUTO.

 

This makes me wonder if there is not a much better choice of pump to use (and possibly much less expensive) if I have to replace mine,
and if there is a better solution than the valve used (it is really squeezed in there... a poor design implementation, with the inline check valve there is not enough room for the heater outlet hose to make the bend)