Recent development, the AC is on all the time, no matter what temperature it is set to or what mode (other than OFF, it does turn off).
I suspect the cabin air temp sensor, does anyone know a way to test it?

Thanks!

 

Hi hepcat ,

a few questions pop up, mind if I check? You say that you can turn it off if you push ac button ( light goes off) . Did I read that right?

I was about to ask how you know its on, but let's run a few things. From what I've learned, these car's will enable the AC whenever the auto function is chosen except under a few circumstances. This is intentional to deliver (what's the right term?) Conditioned or comfortable air.

what are those circumstances ? Outside temperature drops to the point ice could form on a.c. components (on other cars I've owned that was down around 40 degrees Fahrenheit); car's coolant approaches overheating temps; you initiate WOT ( wide open throttle).

is it possible that your car is operating as designed?

John

 

As a newbie, you cannot yet ownload attachments from the forum so there is no point in me posting the full diagnostic procedure. However, the initial Functional Check will help indicate whether yourt AC is working as designed or not:



If the AC is delivering air at the WRONG temperature, a possible cause is a fault with one of the three sensors:




The usual culprit is the In-Car aspirator (item 2) fitted behind the plastic grille in the bolster below the dash on the driver's side. This is the location on my RHD 2005 XK8:




Graham

 

I thought the temp sensor, on UK cars, was on the other side, left, of the steering wheel? Isn't that where the switch would sit for the car-distance in front radar (or what ever its called)would sit?

 

Thanks for the replies, I have tried steps 1 -10 of the Functional Test as a matter of course in my first attempting to diagnose the problem.
How is step 11 performed?.
The AC blows nice & cold, I am in Florida so even in December we are having temps in the 80s (F).
The AC was previously functioning properly, now even if the in cabin temp setting is set to 90 degrees and it is actually 70 degrees it does not cycle off. The compressor clutch is functioning properly, toggling the AC switch engages / disengages it.
I have already checked that the In-Car aspirator is securely plugged in (I was calling it the cabin temp sensor, if I understand it correctly there is a temp sensor part ((#5)) and a fan part ((#1)), this is the assembly part I was hoping to find out a way to bench test for proper operation.
The outside temp is reading correctly, am I correct that this means the solar sensor (#4) is working?

 

Update, I found the in car diagnostic online, it is reading fault 11 & 14 (in car temp sensing fault & coolant temp signal fault)
I think "coolant" in this case means refrigerant?
Is there a refrigerant temp sensor on the line-set I can check?
The suggested action for the temp sensor is to check for high resistance, short to ground, and B+. I will decipher the wiring diagram for this and check.

 

My 2001 XK8 also had the In-Car sensor on the RH of the steering wheel:



Graham

 

Good to hear you found the full diagnostic online.

NO - I'm sure coolant temp signal refers to the Coolant Temperature Sensor. There isn't a refrigerant temp sensor.

Graham

 

I JUST cleared the CC codes yesterday (was having your same problem) and it seems to have resolved the issue- I get hot air now.

 

I removed the in car air temp sensor (#2) and aspirator fan (#1) and bench tested them, the temp sensor reads about 1.8K ohms at 70 F and goes down in resistance when heat is applied, and I put 10VDC (being a little cautious) to the fan and it spins so I think they are both good.
Clearing the codes has not fixed the problem, but I have yet to get another error code.
Hmm...
Can someone tell me where the ambient air temp sensor (#5) is located? I am guessing near the front grill?
As far as I can tell, the solar sensor (#4) is not connected to the CCM, it is part of the lighting system.
We are getting a cold snap tomorrow, I will see if I can get the heat to work.

 

Ambient air temperature sensor is behind the front bumper. You will have to remove the Undertray to see it.

I'm starting to suspect the Heater Pump has failed.

Graham

 

You may be onto something, it was about 50F here yesterday and I am not getting ANY heat. (AC clutch still ON constantly if in AUTO or AC mode at all times no matter what the temp is set to).
I jumped the pump relay & I hear it spin (I read that the motor can spin but the impeller may be stuck as it is magnetically coupled) and the relay tests good.
It looks like the next step is to check the valve () and try flushing the core...
Back to the original issue, no change.
I see the solar sensor IS connected to the ACCM, does anyone know how to test it (and where to get to the connector?)
I can't find the heater pump & valve in the wiring guide?
I also see an evaporator core and heater matrix sensor, any info on these?
Is it possible the the ACCM would not show any errors, control the obvious functions, but still be faulty?

 

I had a broken Solar Sensor (arrowed blue) on my 2005 XK8. The connector was under the Facia speaker grille (arrowed red):




Taping a length of string to the harness was the only way to pull a new one through.

Graham

 

Can anyone verify or refute the specific point that the AC is supposed to be always enabled in auto mode, regardless of set temperature? That's not completely nuts if the AC is supposed to be always conditioning (for example, dehumidifying) the air even if it's then passed through the heater to warm it back up.

The way I understand, @HepCat1 is seeing that behavior, and @Johnken brings it up in the first two comments. It's something I've wondered about since hitting auto on my '97 engages the compressor even if I'm setting it thirty degrees above the external temp.

Maybe that's actually expected functionality?

 

Not saying yours is not there but you might find this an interesting read :- https://www.jaguarforum.com/showthre...=1#post1145503

 

Regarding the Aircon not switching off. Still a little puzzled. My aircon automatically comes on and stays on if I push the Auto button. The next obvious way is to turn on the heating by pushing in the left knob then pushing the AC button. Are you saying that it comes on and stays on if you do none of the above?

 

Let me preface with stating that the climate control system in my car was working correctly and now is not. I could set a temp and it would maintain it.
Now it is freezing cold if the CC system is on and AUTO or AC is selected, even with the temp control set all the way up.
If the CC system is on but neither AUTO or AC is selected, I get no heat regardless of the temp setting.
I see this as indicating 2 problems, the AC compressor clutch control is malfunctioning and the heater core is not getting engine coolant flow.
I have dealt with many HVAC systems, they all worked by turning the compressor on & off to maintain the desired AC temp. All the modern auto systems I have dealt with work this way, and many keep the engine coolant circulating through the heater core at all times and use the flap system to control if cabin air is circulated through the core. They allow for heat & AC to run at the same time when a defrost option is selected and direct the AC to the demister vents.
The XK8 / R wiring diagram 2001 shows the AC compressor clutch relay coil power is controlled by the ECM (so it will not engage with the engine off) and the contacts switch the B+ signal from the CCM to the compressor clutch to turn it on & off.
Are you suggesting that this system works by constantly running the AC compressor if AUTO or AC is selected? How can it maintain a cooling temp if this is the case? By using the heat to offset the cooling?
Methinks this would be an extremely inefficient approach, vastly increasing the fuel consumption and prematurely wearing out the AC compressor.
I can find no programming flow chart for the CCM so I do not know how it's program is designed, but it appears that in standard AC mode it uses the in cabin air temp sensor input to control the cycling of the AC compressor and maintain the set cabin temp, and in AUTO mode it uses the in cabin air temp sensor, the ambient air temp sensor and the solar sensor to decide when to cycle the AC compressor on & off and direct air through the heater core.
Is this correct?

 

Hepcat, I think this thread went in 2 directions.

1) I thought your original question indicated the ac was always,on when the ac button was lit. I suggested that from what ive learned it should be.

2) your climate control is malfunctioning, you've requested technical assistance that I missed when I answered in the beginning.

now we are discussing #1. You made good points. Looks like there are still a couple of questions open around #1.

How does the climate control maintain selected temperature, say 70 degrees Fahrenheit, in a 80 degree environment without taking the temp too low? (IOW what stops it at 70?). Does the compressor cycle on /off? Does ccontrol mix hot and cold to deliver dehumidifier 70 degree air?

regarding the statement ac is always on with auto selected, I think there was some push back pointing out that would be incredibly inefficient. Good point. The ccontrol will dehumidify air as long as the air passes cold ac components and they'll stay cold with compressor off for a bit.

given what I've read, the ccontrol aims to deliver dehumidified air as long as auto is selected. There are several stated conditions that will shut the compressor off (overheating, WOT, cold outside temps). I guess the statement always on is then wrong.

It must then cycle the compressor and carefully mix hot and cold air to achieve and maintain the selected temperature. So the statement always on isn't technically correct. Maybe it should say always working to provide dehumidified air at the selected temperature .

John

 

I do think that in AUTO mode AC is always ON (but the compressor clutch is only on when the system decides it should be to maintain the set temp).
I have noticed the following:
When AUTO is selected, the fan comes on full speed. Lowering the speed cancels AUTO mode.
When Auto is selected, turning AC off cancels AUTO mode
Do other's systems operate this way? Are there any controls that when selected do not cancel AUTO mode?

Thanks again for all the input!

 

Have you checked the external temp from the display? Does it display something close to the actual temp?

My sense is that the AC cannot "beat" the heat. If there is heat coming in the core, the AC cannot make the air cold any more. My focus would be on why there is no heat coming out of the vents. Check the 2 heater hoses going to the core from the engine compartment. You should be able to touch them and feel for heat. If there is heat, then the core likely needs to be cleanup up (I did a few weeks back, and the result was pretty dramatic). If there is no heat, and you have checked the heater pump actually runs, then disconnect the valve (it defaults open), then see if heat comes in. Obviously, a laser thermometer is great for this, but not completely necessary.

Separately, forget about "Auto" for now. If you put the temp on "HI", and control the fan manually, do you get heat? Also play with "Recirc" for more info.

Best of luck, keep us posted.