A gentle word of caution. You may be entering the "Paralysis by Analysis" zone. I had a hard time making sense of all the values you posted. Sometimes it's possible to have so much data, one doesn't quite know what to do with it all.

I must admit I am confused about the temperatures you recorded on the suction and discharge lines. Take a look at this generic diagram of the refrigerant cycle:



The suction line, where you recorded 230F, is at the 11:00 position. This is where refrigerant is returning to the compressor.

The discharge line, at 180F, is at the 1:00 position.

Are you positive about that 230F value? Maybe you have the lines mixed up? In a normal world, the compressor inlet should be cooler than the outlet, yet you have the opposite by a substantial margin. Is there an adjacent exhaust pipe heating up the line? Could that be something funky, such as a failed check valve at the compressor inlet pumping heat back into that line? I don't really know, just thinking out loud.

Also, you took this reading when the behavior was "wonky". What about when normal? I'm still leaning towards my theory of either a mechanical problem with the compressor causing it to run hot, or a defective thermal switch activating early causing the compressor to shut off.

 

Line temps checked 4 times and verified the right ones. The suction line about 18 inches leavinh the exp valve is 155f. I am positive i am checking correctly. Line temps leaving the evap to compressor should be 60 to 80 with 30 to 50 psi normally. I too do not know if the comp can reverse and cause these problems. 2 cans freon is 20 bucks so no biggie there. I am going to blowout the valve and add a little oil to the comp for safety. Recharge and see what happens. Putting on a new compressor is way easier than the valve. I would replace that next and check again. The only reason i do not replace comp at this time is my back. If needed that is 2 weeks out. This is similar to the trans issue i fought recently. Ghost data that made no sense and fixed by a non trans repair. I do know enough about these types of valves that they operate slowly

 

i think the thermal switch is fine. When ac operating good the suction temp is 70f and discharge is 120f. I too was baffled by the odd temps at failure but i verified lines and did it 4 times. The car has 188,000 miles on the comp so replacement is warranted by mileage alone. I will save the txv as a last resort because of the teardown involved. The windshield cowl and brace has to be removed for access to the txv. I can leave it off and drive the car if my plan to blow out valve fails and then comp replacement fails. 2 more weeks of my back getting stronger is all i need to take on the comp job. It will take that long to do the valve blow and get the new compressor
big edit. Those good line temps are from my truck with good ac for comparison. Sorry i left that part in my head

 

I'm still leaning towards my theory of either a mechanical problem with the compressor causing it to run hot,



i am with you on this Karl because of how strange and odd the line temps and pressures are from the get go. Plus mileage and quantity of metal shavings i found

 

Yeah, but I'm still kinda hesitant to recommend an expensive gamble. Wish I had a more definitive answer. I'm fine recommending a $15 sensor or something like that. No big deal if it doesn't work out. But considering the expense of replacing the compressor, have you thought of taking the car to a shop for a professional* diagnosis?

I suppose all things considered, the compressor is still the most likely culprit. You've confirmed everything seems groovy for a while, and then after the a certain amount of time, suddenly the compressor clutch kicks off and all cooling ceases. Furthermore, you've confirmed the thermal switch on the compressor is opening to shut off the clutch. There's a slim chance the thermal switch is activating too soon, but most likely the compressor itself is the root cause.

You had mentioned the possibility of the thermal expansion valve being bad. As difficult as changing this part is supposed to be**, it's probably best to rule out other possibilities. I did look up the symptoms of a failed thermal expansion valve, whether stuck open or closed. Here's a good description:

https://www.carparts.com/blog/bad-ex...alve-symptoms/

"An expansion valve that’s stuck open can result in a flooded evaporator core, which can cause frost to accumulate at the evaporator’s outlet. On the other hand, frost buildup on the outside of the expansion valve can indicate the valve is clogged or stuck closed."

So reading between the lines, if the valve failed (whether open or closed), you'd get frost accumulating somewhere.


*Someone to blame and hold financially responsible if wrong.

**The thermal expansion valve is the first part down the assembly line and the car is built around it.

 

I got the comp new for 200 delivered so that is the price of a diagnostic. I will go by the old phrase. It needs it anyway. Ac performance has been slowly dropping for about 2 summers until this failure. I did a vacuum and recharge at the end of last summer but no bag. It helped some but the problem of ac shutting off for a bit has been slowly getting worse. The comp replacement is pretty straight forward and i am comfortable with it. So i start there. If i have to go after the txv then that is way more involved and tedious. I will know sometime this weekend. Thanks again for all the help everyone

 

Update. Took off old comp and when i turned it by hand it just freewheels like the clutch bearing. Insides are shot. The new one of course has the pump feel when turned by hand. I have it buttoned up and pulled a nice vacuum of 29 inhg. Sit overnite and finish tomorrow. I am beat. Two issues that were a nightmare where getting old comp out. Had to wiggle and twist and move lines and finally out. Second was getting the ac manifold bolted square to the comp. Somewhere along the line i messed up the angle of the manifold. I fought and fought and was about to give up when i pulled back the wheel liner and split the suction line at the peanut fitting and split the high side on the wheel well under the hood. Then it was easy to square it and the peanut fittings took up the slack. Pulled a vacuum and was ecstatically happy. More tomorrow after finish. The more i think about it after checking old comp i think freon was just barely moving by the comp or moving on its own for a few minutes. No matter. It is done. I would rate this as toughest repair i have done on this car. Replacing torque convertor is close but i made some mistakes that cost me time and effort on that one. If anyone wants the old comp to do a teardown diagnostic you can have it.

 

Yes, its a 'tough repair' on the STR. More so on your LHD vehicles requiring the steering column to be dropped as well.
I was dumb enough to end up doing it twice, three months after the first time. Second time around I removed the front bumper which made for far easier access when doing it on the garage floor.
Per usual, wasn't too bad second time around as your brain 'knows' as its been there before.

There was a second time around because I had the factory compressor 'reconditioned' rather than buying a quality aftermarket unit.
Was reconditioned by a known expert but these units don't recondition well due to difficulty of obtaining some of the internal parts.

All will be forgiven when you turn it on in the hot Californian sun.

 

i basically folled the jtis and dropped the steering rack. Pretty easy. Then when lifting the engine it stopped cold. Took me a bit but found it was the big intake pipe to throttle body. I have the larger range rover one so i removed the windshield cowl and cross brace and had plent of lift. It just took hour to figure out the way to get old comp out. New one went in fairly easy. I tweaked the manifold block and finally figured out how to square it after an hour. So much subframe steel on the R. Makes for a double tough repair. I have to replace the dessicant bag still. But that is pretty easy. The vacuum again as i button up the engine stuff. Wish i had some time saver tips but none come to mind other thanif the ac manfold doesnt seal square undo the suction and high side peanut fittings and it will pop right in. One thing i did was lift the engine where the tranny and engine housing meet. Way stronger and no chance of breakage or crushing sheet metal

 

Going outside to finish now. I do have a couple tips that may be new. After new comp is on with lower bolts holding it and engine still raised. Put on the drive belt now. It is way easier. Especially on the R model. The indexing spacers that are on the factory comp can be removed with pliers and put on the new comp as it is indexed to use them. Reusing the index dowels makes it way easier to square the comp to block. Also tighten the bottoms bolts all the way then loosen a half turn before you lower the engine for the top bolts. That way the top bolts will tighten and seat the dowels then you can tighten the bottoms with an end wrench and be bolted up

 

Well. Good news is i have a new ac compressor. Bad news is same problem only now it shows up quicker because comp is working. I got the full charge in but now with comp running at 2500 rpm it pull about a 28in vacuum on the suction side. The case superheats and thermal protection shuts it down. There is a blockage somewhere and i still suspect txv. I may check a shop or 2 for a diagnostic quote before i proceed. I have taken r8 relay to the ac clutch out so not to inadvertantly have ac commanded on and mess my new comp up. For now it will be thinking time. I will not empty the system again until i have let a pro look at it

 

No frost build up anywhere. Does that point to possible jammed condensor. Thinking out loud

 

Well, that’s a pisser. I was hoping to hear something more along these lines:

”Karl, you’re a genius and a credit to humanity. The world is a better place because of you. I’ve heard you’re good-looking and I bet you smell nice, too.”

We are definitely getting outside my area of alleged expertise with AC systems. I think a professional diagnosis is probably your best option.

Any thought to the new compressor being defective? Did it include a new clutch and thermal switch, or were those swapped from the old unit?

 

no worries Karl. Everything you say has tidbits of info. Yes. All new on compressor. I turned it by hand and felt the inner workings doing their thing. The old one was like spinning a free bearing. Plus the amount and size of metal pieces were from the old comp. I put in a new dessicant bag last week and when i replaced it it was covered in shavings. I am going to take some condensor temp readings before i go pro. Taking the bumper cover down is easy and about 15 mins for clear access. Those temp readings will tell a lot. This is forever car to me so refurbishing the ac is not a worry. I will keep following the refrigerant path and i will get it. I fought a trans issue for 3 years. This is cupcake compared to that. Well. The comp replacement itself was excruciating but it is done