Hello all
recently my ac has been acting up. At first it was needing a throttle stomp to get it going. Then at low rpms getting weak but at road speed nice and cool. Then i noticed the compressor being commanded off for a period then back on. I decided to replace the dessicant bag thinking it might give a clue. Well the clue is a black bag with shiny sprinkles all over it. I guess a compressor is needed. I am a month removed from back surgery so that will have to wait. In the meantime i did the comp valve reversal and spring. I also vacuumed for 3 hours and then held vac for 3 more. I charged the system and it works good enough at higher rpm. Any insight or tips or anything is always welcome. I think the new bag will at least catch stuff. 2006 s type R 188,000 miles. The comp still kicks off after a bit and i suspect it is the ac protection working. Then comes back on and blows cold. Swapped relays and same outcome

 

A few quick thoughts:

The presence of minor metallic debris is normal to some extent, indicative of regular wear and tear. How much is too much? Hard to say, but a little bit is not cause for concern.

If the compressor had failed internally, with performance dropping off, the clutch would be commanded on all the time. But since it is cycling off, the compressor may still be okay.

I’d have to put on my orthopedic thinking cap and work this through a bit more, but my first impression is the compressor may not be at fault.

 

i would classify the particles as quite a lot. The other thing is that the rear of the compressor gets smoking hot. I mean untouchable. I have zero experience with scroll compressors. All mine is piston type. If they ever got that hot it would mean lockup time. I am thinking mine is like on its last leg. Maybe it will not fail completely. When the compressor shuts off sometimes i hear a sound similar to a pressure release. A pffft if you like. It is hard to position the gauges to see them and work the throttle. From what i can see the high side looks normal at all rpms. The low side is about 80 to 90 at idle then after about 2000 rpm the air gets colder and pressure goes to 40 or so. Higher rpm continues to drop low side pressure to almost 10 or lower from what i can see. Then the pffft and compressor off. I am thinking the low side protection is at the compressor. Again. When vacuuming it pulled down quickly and held nicely

 

Here are photos of both sides of bag.The metal specks are more visible in person. Another clue i just found and remembered. Yesterday ambient air was about 105f and ac was sporadic after repairs. This morning ambient is 85 and ac works perfect. I remember doing some temp checks while driving and it seems the ac acts up at around 103 or so ambient. I know for sure once when it was 101 i kept watch on ambient and the ac worked perfect when i first noticed the problem and began to gather data. At some point the ambient temp corelates with ac acting up. Engine fan spins at high speed or whatever commanded perfectly. Maybe the condensor is plugged slightly. The condensor is in front of the rad so engine coolant temp should have little to no affect on condensor cooling capability

 

At first I thought this was a big clue, but I got to thinking more about it. I'm not sure how warm the compressor normally gets. At 200 PSI, a normal value on the high side, you'd see 130F. That's going to be toasty hot to the touch.

That may be the sound of the clutch slipping for a split second as it releases. I can barely hear it on my car, but it's very noticeable on my truck.


There's no actual low side protection. As long as you've got some oil present (carried along by the refrigerant), the compressor can run at low pressure all day.

Now, the compressor does get switched off to limit ice accumulating at the evaporator. Unlike most systems, there's nothing directly measuring low side pressure. A temp sensor takes a direct reading at the evaporator, versus inferring the temperature based on pressure.

The only "protection" is the AC pressure sensor on the high side. If pressure gets too high, the compressor is switched off before things explode. It's a dual-purpose sensor and also kicks in if pressure is VERY low, to protect the compressor from running without the oil present in the refrigerant flow.

​​​​​​​Bored you silly yet with all these useless details? I still don't know what's happening. I predict the brilliant answer will come to me around 3PM (Pacific time) this afternoon.

 

Great observation. I think you may be on to something.

Can you reliably duplicate the fault? There is a thermal switch on the compressor. Above a certain temperature, the switch opens and shuts off the compressor clutch. Take a look at post #5 in the troubleshooting guide:

https://www.jaguarforums.com/forum/s...2/#post1714574

It shows how you can easily measure the resistance of the clutch coil, all from the fuse panel. You unplug the relay and connect an ohmmeter to socket #5 and ground. When cool, you should see approximately 1.4 ohms through the coil. Measure this to be sure. Then reinstall the relay and run the AC until the compressor kicks off again. You may have to do this on a very hot day to duplicate the fault. With the fault active, quickly shut off the engine, remove the relay, and repeat the measurement. If your meter now shows no continuity, then you know the thermal switch had opened up.

I don't have any details on when the switch opens. Also don't know if it is replaceable separately, in case it is activating early. Nor do I know what is considered a normal temperature at the compressor. But spend 5 minutes with a meter and we should have some idea.

 

I did have my head next to the comp underneath the car when i hear the noise and cannot hear it standing by the drivers door. Think you pegged that one. As far as comp case temp i think it is way high because i accidently just grazed it with the back of my hand and instant blister. Like i say my experience is late 80s and older old style systems. I am a little leary of the low side pressure at higher rpms. But that is using my knowledge of the piston compressors. Maybe the scroll operate the way i am seeing it. I know this system pulls to 28 to 30 inches vacuum way quicker than the old style. Just took a drive at 94 ambient and all is good. I think i will let the car cool off and blow out the condensor as best i can. To do it right i really need the bumper cover off. I am pushing my luck so i need to be careful. Only a month removed from L4 to S1 spinal fusion surgery. But wow. I can really feel a positive change in my spine. Stronger. No more leg pain. And i am 6ft 4in again and the creeper is my friend again

 

i will do this check and i bet you put 2 and 2 together

 

This is my r8 ac relay. When cool and normal i get 0.1 ohms on 3 and 4.6 on 5. When the clutc disengaged i turned car off and got open or OL on both 3 and 5. Comp overheat is working it seems and opening the circuit. Makes sense on how hot the comp gets. Maybe 3 goes to clutch. No matter they both go open when clutch disengaged. Looks like comp is failing. Especially since i have to goose it to make it work. I dont think i have a low oil case but anything is possible. I could add some by splitting one of the lines but then another 30 of freon on a guess. Thanks for the help Karl. I would have never found that route. At least all the protection is working. Two options. The comp is ok and i have a restriction and causing overheat or bad comp or third is both. This issue will rest until my back is another month into healing i think

 

In my esteemed ignorance or lack of memory i forgot how the flow of refrigerant goes in automotive applications. The compressor pumps into the condensor not the other way as i had in my head. I now think my condensor is fine based on the pressure i see. Very clean fin passages also. If there is a restriction on the suction side it would be evap core or expansion valve. Next time i open the system i will used compressed air and do the reverse blow back i have read about. If i do anything before compressor replacement i will do that and add a bit of oil and see what happens. I will also verify correct operation of dccv because it is original as far as i know. Any insight or tips no matter how obscure is always welcome. If whoever knows the air blow procedure could you kindly post it. Thanks

 

Actually, relay socket #3 is a hot battery supply. You should see battery voltage there at all times:



Socket #5 is where you measure continuity through the thermal switch on the compressor. Just to be sure, at the panel, you were measuring 0.1 ohms between socket #5 and ground when all was good, right? That is reading the switch and coil in series. On my '02, i measured 1.4 ohms but that minor difference could be from different meters or model year changes.

When you got the compressor to kick off, the same reading changed to OL, meaning no continuity. If so, with the same meter setup, that's definitely the thermal switch responding and opening the circuit.

Considering the compressor was hot enough to give you a blister, most likely the thermal switch is operating properly and the compressor is failing. Might be something like a bad bearing overheating.

 

Yeah i figured that. There is a difference in my relay and the one you show. Mine has only 4 prongs. That is why i took a photo so you could see the relay diagram. But yes. Continuity verified when compressor was cool. After compressor shut off i turned car off and had open circuits verifying ac thermal switch had activated. I know that on the R model at wot or heavy acceleration the ecm cuts off ac operation. Dont know about other models. Used the 2006 s type wiring from gus website to id relays. Owner book only covers fuses. I was going to temp check the comp case with infrared but forgot. If i have it on ramps again i will do that and post the info

 

This is pretty common. Look at the diagram I posted earlier. In this circuit, socket #4 is not used. Some OEM relays don't even have a #4 prong, to save the fraction of a cent it would cost to include.

Most aftermarket relays do have all 5 prongs, even if one of them isn't needed in many applications. You can use a 5 prong relay if only 4 are needed, but not visa versa.

 

Quick extra. Ohms on socket 5 was 4.6. I guess the clutch coils is wonky also

 

Not necessarily. On my '02 V6, I measured 1.4 ohms, but all that means is you are comparing your clutch coil to the smallest possible sample of one. For all we know, mine is out of tolerance.

 

FWIW, to compare apples to oranges, I took a quick temp measurement on my car today. Forgive me for not raising the car and crawling underneath to read directly at the compressor. Instead, I measured the compressor discharge line, where it enters the condenser.

75F ambient, manual LO so the compressor was running, I measured 150F on the line. It would have been slightly warmer where the line left the compressor. I'm guessing the compressor case would have been similar.

Might be worthwhile to shoot a temperature reading on your compressor. If comparable, there's a possibility the thermal switch is defective and opening too soon. I don't even know if this switch can be replaced in situ. If this is possible and not too expensive, it may be worth a gamble.

 

i know Karl. Just hoping. Trying to weasel a way out of compressor replacement. Wanting that super light bulb in your head to save me. Looks like my 12 mpg chevy truck will be up to bat for a bit. That is ok. It needs driven some anyway. Until my back heals a bit more i have no where to go anyway. Thanks as always

 

Good troubleshooting and suggestions.

You bag was much dirtier than mine? I had only 60K miles on my XJ compared to your much higher mileage so maybe normal? I was concerned how black mine was at 60K and by the fine Aluminum particles I found along with the bag.
Here is the new one next to the old one.




Here was the bottom plug of the filter/Dryer and you can see the fine metal particles. On my 2014 XJR the bottom plug comes apart and has a small screened in area that apparently is for catching these small metal particles?




There was so much I tapped it out on the bench top. Took a picture and tested the powder to make sure it was Aluminum.




So with the high miles you have I would go ahead and replace the AC compressor. I think you got your money's worth out of that one! All the metal you found might just be an indication of 188K miles of use?
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Ok. I think this info will pinpoint the problem. After about 15 mins of ac on the troubles begin. Ambient temp not a real factor. In morning at 75f ac works for about 15 mins. This afternoon at 95f. Same thing. Here is new info about line temps and pressure. When ac is wonky line temp on suction line is 230f. The discharge line is 180f. Case temp is 210. I know the temps go higher the longer is runs. When ac is cooling good at 3000 rpm the suction side shows a reading of -5 to-10. At idle about 50. The high side is normal at 225 at 3000 and less at idle. The biggie is when the car turned off the static pressure is 150 and at shutdown the low side immediately to 150. Not slowly like it should. This also happens when car is running and compressor turns off. This is pointing me to the expansion valve closing after a bit and putting the suction side into a vacuum and causing the superheat condition causing the thermal switch to activate and basically no freon movement even when the compressor kicks back in. It just cycles to superheat again. Eventually after a shutdown the valve goes back to normal but the whole scenario starts again. From what i have read all my symptoms are pointing to the valve closing completely after about 15 mins. I rule out the compressor or evap blockage for now because of the 15 mins of perfect operation no matter what ambient is on a first startup

 

This problem has been slowly manifesting itself for a few months. Gradually getting worse. Now the slow failure makes sense with all the data i have detailed. I could not pick it up on a vacuum with the pump because the valve is normal then. I may still do the comp to cover all bases. The valve is a bear i have learned. We shall see. I do not know if the comp can act up and push discharge thru the low side. If so i would think it would be that way from the start of the car and not 15 mins later