Many thanks for responses.
I have not seen any warning lights on dash. The car in in Florida and is a US type car. I have not had any codes pulled. The AC is not cycling rapidly and it is not the same amount of time between cycles anyway. Sometimes it can be 15 seconds and sometimes more than a minute. This probably removes the lack of freon idea correct?
I'm still now betting on a sensor if you agree but don't know where it is located and whether it is something I can change myself? Should be a cheaper option than an AC unit though if that is what it is.

 

If the a/c is cycling in 15 secs then almost certainly it's cutting out on the low pressure switch as the suction side pressure drops - do you have cold air blowing from the vents? Only sure way to tell if you are short of gas(unless of course there's an obvious broken pipe in which case it's short of gas(old refrigeration industry joke)) is to fit a charging manifold and check the static and running pressures - that's the only way to eliminate guesswork.If the system IS short of gas that would reduce the load on the compressor, not increase it, unless it's full of air in which case the discharge pressure and temperature will be high BUT it can't be because the LP switch will interrupt the compressor energise circuit to stop that exact event - that's its function in life.In all practical terms the only way that air can enter the system and cause high discharge pressures is if it hasn't been correctly evacuated and charged in the past.
Have you removed the serpentine belt and checked for roughness/noise on the clutch bearing - quick and easy to do. If that checks out fine then it's pointing towards something on the engine management system that, as has been said previously, should compensate for the increased load when the a/c cuts in. If the system is short cycling then almost certainly it is short of gas but that on it's own is unlikely to be causing your engine stall problem.

 

Thank you for your reply. The AC can cycle as low as 15 seconds but more normally it is 30 to 60 seconds.
I have air as cold as you like from the vents.
I will check the clutch bearing and belt for roughness over the weekend, what/where do I have to loosen to get this off please
Phil

 

I have checked the belt and whilst it has a few minor cracks that I can see in the ribs that are exposed it doesn't look bad or loose. I cannot see how or where to loosten it to check the bearing. What a difficult area to get to with so much in the way. Think perhaps I need to get a garage to check it.

 

The idle system in this car involves the throttle stepper motor in the throttle body and the ECU. When the AC is switched on, the ECU sends a signal to the throttle motor to open the throttle until it raises the rpm to a preset standard and holds it there. When the compressor cuts off, the ECU closes the throttle opening until it switches back on. In older cars with direct throttles, the ECU operated an air bypass called an intake air controller, which opened and closed an air passage around the throttle plate to do the same thing. My concern is that your throttle body may be having a problem. I would look there.

 

Two suggestions - check the air con codes as advised earlier and clean the throttle body.
Both these procedures are described in the HOWTOs at the top of this section.
It is possible that the throttle is sticky and not opening on command.
It doesn't sound to me as if there's anything wrong with the compressor.

 

I must be blind as I have found the HOWTO's section but can't see one on cleaning the throtthe body. Am I looking in the right place?

 

Here it is
http://www.mediafire.com/?43rs029k5l7uici

 

PtheB: oldmot has a good point about cleaning your throttle body. If the idle circuit is located there it could be effected by a partial plugged (with sulfur residue from poor gas) throttle body. You can be assured that Jaguar will charge 5 times what it’s worth or refuse to do it at all, but I’ve done enough such throttle body cleanings to know that they work magic if there’s a blockage there. It doesn’t take much to throw off these minutely calibrated system.

Here’s a link to a good and easy to use 3M DIY product that could hardly be cheaper or easier to use. Give it a try before you lose any more hair over this.<G><G>

http://www.summitracing.com/parts/trm-8963?seid=srese1&gclid=CNuxpdrRmLcCFcuh4AodOiMASA


Here’s video showing how it’s done.

 

Firstly let me say that my AC cutting out the engine problem has gone away. I don't know if it matters but I did not mention that this car remains idle for three months at a time when I go back to UK. I know mechanical things can be tempermental under these circumstances. Anyway without doing anything it now works perfectly at all revs including idle.
Secondly I cleaned out the throttle body today with some throttle body cleaner, have to say it was quite clean already but there was quite a bit of sticky residue lying in the bottom of it.
Lastly I really struggled to get the clip undone on the part load breather on the drivers side so I left it rather than break it.
Thanks to all who replied, you were all most helpful.

 

Yessh...this kind of wild goose chase is what happens when we don't get the whole story. Imagine a service technician trying to sort through this without an important piece of evidence .