Old Delphi CVC-125 variable comp (TXV system) exhibiting a strange behaviour

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Al9
Posts: 114
Joined: Tue Mar 10, 2020 3:26 am

Old Delphi CVC-125 variable comp (TXV system) exhibiting a strange behaviour

Postby Al9 » Tue Mar 10, 2020 4:44 am

Hi everyone. Great forum, read almost all threads and learned a lot of valuable info.

My car is an European MPV of Japanese/German descent, known as the Vauxhall Agila A. It has manual HVAC, a block type TXV, pretty the same evaporator of an early 2000s Chevrolet Tracker, and sports a Delphi CVC-125 variable displacement compressor equipped with the same mechanical control valve found in any Harrison V5, the blue one (42 psi rating) in this case. R134A. It's now about 17 years old but it still seems to have a functional shaft seal (no oil is visible around it, no oil is slung around), additionally all old o-rings have been replaced across the system and a new liquid line (an idiot damaged it while in a shop) and pressure transducer have been fitted along with a new condenser and dryer and new HP and LP valve cores. It also has a new control valve (UAC EX 10458C) and a new HPRV. During the liquid line, condenser and dryer replacement, done all at once, 2 ounces of double end capped PAG 46 oil (the required viscosity for this compressor, even though, in retrospect, i think 100 would have been better since the compressor is old) were refilled. I got the old dryer back and it had a little oil inside, but definitely didn't look overfilled.

It's only been ran on a painfully low charge (in grams, 220 grams out of the normal 500 ones) about three times in its life, but never to the point where the TXV started hissing audibly, and it has suffered about three clutch coil thermal fuse failures (later discovered a clutch coil connector was faulty ECU side, and replaced it), with all clutch coils looking in mint condition, never saw any burn mark on them anywhere, and the clutch hub (the one with a rubber ring and three rivet looking things all around) seems to be in a perfect condition, no signs of rust/clutch material anywhere.

Last Summer, the control valve failed and started keeping the compressor on a low displacement even in 80F-90 F weather, and really cold air came out only while barreling across the highway, especially under the sun. Also, the engine didn't seem to exhibit a large load from the AC, all of this even while the system was correctly charged with the required 500 grams of refrigerant. Also, the evaporator emitted growling noises while cooling was acting up; additionally, after parking the car with a warm engine, restarting the AC yielded a really loud groaning noise and the system absolutely struggled with cooling until you started speeding around. Found out later that these noises were caused by the system running a positive evaporator superheat while the compressor was in low stroke (a reed valve vibration that makes the suction pressure pulsate, basically), so basically i positively concluded that something somehow starved the evaporator at high heat loads. It either had to be the TXV or a control valve, since the system didn't show signs of obstructions (took temp readings everywhere). A new control valve with a matching suction pressure rating was then ordered and fitted, and with the new one inside the system started behaving much better than before, placing the usual engine load in hot and humid weather, becoming almost whisper quiet and reliably outputting cold air.

However, sometimes the compressor seems to be noisier than usual, and it will still struggle with cooling in these cases. For example, starting the AC as soon as the engine is on, and driving with it on, results in reliably ice cold air and an almost inaudible compressor even as the engine warms up. If you then leave the engine and AC on, park the car, get off and get in front of the engine bay, you will hear the compressor running destroked (correctly so, since you're getting ice cold air inside and the evaporator shouldn't freeze up), but the same noise won't be hearable inside, even when you rev it, and even when you stick your hear close to the evaporator's box (almost as if the TXV is managing to run a correct evaporator superheat and the reed valve noise isn't making it inside the evaporator). Turn the engine off and leave for a few minutes so that the evaporator warms up again, then get back inside and turn engine and AC back on, and you'll be able to hear that tell-tale groaning compressor noise inside, and it will struggle with cooling the air down as fast as it did before, then as you drive around it will become silent and cold again. The condenser fan seems to be running cyclically when the engine is cold and almost continuosly when the engine is hot, and seems to revert to a cyclical operation when you put a very low load on the system (recirculation, lowest blower fan speed, closed doors and closed windows). The clutch never ever cycles off while AC is on, except when you go wide open throttle like it's supposed to.
Additionally, if you set the blower fan to a low enough speed and stick your ear under the evaporator box while it's struggling with cooling and emitting noises, you'll hear steady quiet bubbling sounds. Once the compressor has become silent again by driving around, these sounds will go away and you will only get a quiet noise peculiar of a tap held almost closed when you put recirculation on and blower on minimum speed, all of this only hearable under the dashboard a few inches away from where the TXV enters the evaporator box (likely caused by the TXV closing really narrow but not all the way since it's been designed to never ever fully seat closed due to the VDC, and i have very good hearing).

The compressor's head is basically next to the catalytic converter and i guess its heat is somehow interfering with proper compressor operation. I know this compressor always starts running with the pistons fully destroked. It's almost as if the compressor shell heats up due to the exhaust heat, excess crankcase pressure has a hard time bleeding away, keeping the compressor in a low stroke and starving the evaporator as a result.

Can't take any pressures and shops don't seem really interessed, don't look like they have the expertise required to properly check a VDC+TXV system like mine and don't seem to appreciate my collaborative attitude either. They just want to fit a new comp because they think the old one is "worn and tired", however a new original comp is no longer available, and the replacement one is Chinese and also comes with a red (44 psi) control valve (which will have to be replaced to avoid issues), so i'm doubtful it's the correct course of action.

Original TXV is seemingly no longer available either and the closest fit, after thoroughly examining the one fitted on my car (best described as the 4seasons 39056, except for a few differences such as valve lenght, liquid line inlet diameter and bolt holes), seems to be either a Denso 475-0511 (which is used with both a Denso scroll on the early 2000s Echo and a Denso variable clutchless with the Scion Xa and Xb's; so i think it's supposed to be cross-charged, i.e. superheat getting nil once the evaporator approaches 32F, in order to keep both these compressors cool and lubed) or a 4seasons 39128.

All AC services were done through a RRR station, in compliance with local laws which absolutely forbid DIY like stuff such as cans and the like, so i'd exclude oil overcharge or moisture conditions.

Sorry for this WOT, but that's the behaviour i observed.

What do you think about it? Thanks
ice-n-tropics
Posts: 111
Joined: Sat Apr 23, 2016 3:40 pm

Re: Old Delphi CVC-125 variable comp (TXV system) exhibiting a strange behaviour

Postby ice-n-tropics » Tue Mar 10, 2020 8:07 am

Excellent history report and references to comp and txv designs. Your BIG ears cause concerns that most people never consider. Hard to hit the nail on the head by remote analysis w/o pressures.
1) 2000 Tracker had a small Denso evap matched to a sanden SDB very small 87 cc fixed displacement comp, therefore 125 cc at full displacement would be unbalanced.
2) During low charge operation more oil remains in the evaporator and comp lub suffers but the front comp housing did not overheat which would have degraded the shaft seal. 3 low charge exposures could cause increased piston radial clearance and abnormal blow by into crankcase of oil and gas thereby keeping the swash plate angle more than the factory design.5) VDC are noisy at abnormally low suction pressure or low oil return.
You may install service gauges and tape to the windshield while driving and recording pressures. I always disable the wipers.
3) proper oil quantity is dubious.
4) Correct cross charge for super heat management is important for several reasons you noted + stable swash plate angle/displacement to avoid hunting/temp swings. Orifice tube expansion device prevents hunting because the comp control valve is (basically) the only/single flow control device.
6) Excessive OCR (causes gurgling downstream of TXV and may delay comp control valve response to pressure change.Hot comp housing start up should njust be barely noticeable at start up,
hotrodac
Al9
Posts: 114
Joined: Tue Mar 10, 2020 3:26 am

Re: Old Delphi CVC-125 variable comp (TXV system) exhibiting a strange behaviour

Postby Al9 » Tue Mar 10, 2020 9:43 am

ice-n-tropics wrote:Excellent history report and references to comp and txv designs. Your BIG ears cause concerns that most people never consider.

And an excellent answer by your side. And what you tell me is definitely true. Also, you're not the first one to tell me that.

ice-n-tropics wrote:Hard to hit the nail on the head by remote analysis w/o pressures. You may install service gauges and tape to the windshield while driving and recording pressures.

Really hard to do this with my car and where i live. Poor engine bay and hood design for one. Lots and lots of potholes. Random people and LE officers would see me like some really mentally ill weirdo. And laws are really strict about what someone not working with a shop can do. What you get in return? Idiots who pierce a hole in your liquid line and try to place the blame on your car's age (story goes, i videoed everything in the engine bay before giving the car to the shop). Idiots who leave a leaking LP valve core in place without letting me know (another bad story; suffice to say that i'm really wary about handling the refrigerant port caps, since they're really tight and i'm afraid i might damage the expensive piping while removing them, so i don't check them).

ice-n-tropics wrote:1) 2000 Tracker had a small Denso evap matched to a sanden SDB very small 87 cc fixed displacement comp, therefore 125 cc at full displacement would be unbalanced.

Yeah, my evaporator definitely has to be a Denso design. 14 refrigerant channels are visible on each side. You can fit a Denso TXV to it no problem.
I've never seen any brand on my TXV, but i believe it has to be a Calsonic/TGK one, since the evaporator housing is made by Calsonic. The real question is, which Denso valve behaves good with a suction pressure controlled VDC like mine. I hope that since scroll compressors tolerate liquid backflow and operating a low evaporator superheat is beneficial in many ways, any TXV used together with a scroll on other cars is good enough.

ice-n-tropics wrote:low charge exposures could cause increased piston radial clearance and abnormal blow by into crankcase of oil and gas thereby keeping the swash plate angle more than the factory design

Question is, why would it only act up once the engine is warm. Never an issue while the engine is cold. Pull the heater knob (yes, on this car you pull the heater knob, a light flickers on and AC switches on), bamm, all you hear is the clutch clicking in and ice cold air immediately starts flowing out. No further noises. Drive around and you only hear the engine revving, even once it heats up. Maybe the heat from the really close exhaust plumbing increases the piston radial clearances even more? Maybe the cold refrigerant flow is somehow managing to keep them still within tolerance for now?

ice-n-tropics wrote:VDC are noisy at abnormally low suction pressure or low oil return.

True, but in my case suction pressure was abnormally high and the TXV seemed to be fighting against the compressor to lower it. Seemed like the high suction pressure caused by my faulty control valve (Still keep it as a lucky charm btw) kept the cross-charged TXV from de-superheating the refrigerant and this in turn lowered the oil return. I remember the compressor getting real quiet only after having zoomed on the road enough, while it had a faulty control valve. However, after a short while of going relatively slower, you got the groaning noise and the reduced cooling back again. With the new control valve inside, all it usually takes for the groaning noise to completely go away is half a minute of idling, and you'll be always getting ice cold air once the compressor is operating silently.
Also, i distinctly remember having tried to run AC in 43F dry weather in the shade both with the old control valve and the new control valve. Doing this with the old faulty valve immediately resulted in the groan noise and the air not getting any cooler. Having ran the blower with heat on and recirculation on prior to turning AC on and doing it again resulted in a silent compressor start with only the clutch engagement being heard. Starting the AC with the new valve inside with the same ambient temperature and not having ran the heater before compressor start resulted in a silent compressor start and the vent air getting noticeably cooler than without AC on. The same will happen even when starting AC on a hot engine even though the compressor will be noisier. That's another reason as for why i'm confirming a control valve failure.

ice-n-tropics wrote:3) proper oil quantity is dubious.

The only way to check this off is a flush. I'm wary about letting a shop do one for the reasons i've explained. Might end with a seized compressor, a hefty bill and the shop placing blame on my compressor's age. With a new compressor, things might be different, especially if i fill it with 5 oz of PAG 46 right before supplying it and film myself in the process. Drain hole, of course (the CVC has one).

ice-n-tropics wrote:Excessive OCR (causes gurgling downstream of TXV and may delay comp control valve response to pressure change

Doubt about that, since if i suddenly set the minimum blower speed and recirculation on, and listening carefully below the evaporator box, after a very short time, a few seconds actually (the TXV's time constant? Remember it has a really thin metal rod as the actuator), i first hear the compressor groan for maybe 1-2 seconds and then utter silence (can hear the compressor running in low stroke only outside the car, at this point). All of this when running the AC system with a cold engine, when the compressor is reacting properly. I suppose this happens because the TXV first closes almost shut, then the control valve senses the resulting suction pressure decrease, then the TXV opens back again to maintain the low superheat required for oil circulation and stable control valve operation.

Also, i once noticed that if i turn AC on with a low blower fan speed, a cold engine and a cold enough ambient (59 F), such that the condenser fan cycles on and off, noise around the TXV will be completely absent while the condenser fan is off. Once the condenser fan turns on again, the evaporator will emit a quiet sloshing noise that immediately goes away as soon as the condenser fan turns off again. All the while, ice cold air flows from the vents. I also remember that in hotter ambient (80 F and above) the evaporator didn't even make any bubbling noise at all, even while the comp was "misbehaving" as described. It seems as if it's mild ambient (70F and below) which will make the bubbling evaporator sounds appear. All other tests described so far have been done in 70F and below weather. I'll be able to see how it behaves in the next months, provided i'm able to drive my car around of course (you know, that virus thing).
ice-n-tropics
Posts: 111
Joined: Sat Apr 23, 2016 3:40 pm

Re: Old Delphi CVC-125 variable comp (TXV system) exhibiting a strange behaviour

Postby ice-n-tropics » Wed Mar 11, 2020 5:26 am

BIG ears,
Some cars have a heat shield between the back of the comp and the exhaust (Civic). You could try that.
Liquid refrigerant condenses in the coldest place in a static system. In your conditions that is the evaporator where lube also collects. The liquid storage receiver is probably in the hot engine compartment instead of where it belongs forward of the radiator so that all it's liquid refrigerant does not migrate into the evap during short parking times.
You may have excessive lube.
To avoid retained standing water in the evaporator (and mold smell) overnight, I turn off the comp and run the blower before reaching my destination. You might try this on short trips so that the evap is not so cold while you hike, etc. his might reduce liquid slugging that could hinder the comp control valve operation. Some control valve designs have a bypass passage to allow flow of liquid refrigerant or lube. Y
hotrodac
Al9
Posts: 114
Joined: Tue Mar 10, 2020 3:26 am

Re: Old Delphi CVC-125 variable comp (TXV system) exhibiting a strange behaviour

Postby Al9 » Wed Mar 11, 2020 6:53 am

Thanks a lot for your tips.

The liquid receiver (and dryer) is mounted on the condenser and located on its left. Again, it's basically the Chevrolet Tracker's condenser (dryer can be removed and replaced however).
Still close enough to the exhaust header, though. The Agila A has a very very small and cramped engine bay. A Kei car basically.

About the oil, i removed the old dryer from the old condenser myself and opened it with a hacksaw, and although the insides were coated with oil (suggesting oil was circulating around, even though i think my CVC has an internal separator, since the standard oil charge is noticeably smaller compared to one of a V5), oil didn't drip from it as soon as i removed it. Also, the RRR machine removed half an oz of oil during refrigerant recovery right before the condenser+dryer+liquid line replacement. And the system behaved the same way even before this replacement (which required 2 oz of new oil, a quantity which also accounted for the half oz removed during recovery).

However, i second the excessive piston clearance hypothesis and i'm looking for someone i can really trust with a flush, so to check off any excessive oil condition definitely and to remove any compressor wear material that found its way inside the AC system, and correctly install a new comp. The Chinese comp might not be the best way, but it's a new comp after all. I will also test a new Denso TXV and keep the old one with me, to immediately refit it in case i notice high superheat operation (=noisy at low heat loads) or unstable operation (=unstable vent temperatures at low load). It might take years for this to happen though.

Right now, the old compressor is performing satisfactorily enough thanks to the brand new MCV (though not the OEM genuine one; by the way, i've noticed the 42 psi genuine one has been superseded and switched to a brown 43 psi valve for some reason).

Some control valve designs have a bypass passage to allow flow of liquid refrigerant or lube.

I can see such a bypass passage on my old MCV. A little notch that makes the crankcase inlet section (the middle one) communicate with the bellows area.

Last thing, the filter on the old MCV was clean as a whistle. Surprising, since that poor compressor has been severely abused in the past (again, it's never ever been the receiving end of a 100% vapour fed evaporator however).

Thanks again for your insight
Al9
Posts: 114
Joined: Tue Mar 10, 2020 3:26 am

Re: Old Delphi CVC-125 variable comp (TXV system) exhibiting a strange behaviour

Postby Al9 » Sat Mar 14, 2020 3:57 am

ice-n-tropics wrote:1) ...sanden SDB very small 87 cc fixed displacement comp, therefore 125 cc at full displacement would be unbalanced.

In the meanwhile, i came out with another interesting fact about my system. My compressor's PN (09167048) yields both a Sanden SD6V08 1550 compressor (80cc max displacement?) and my Delphi CVC-125. The smaller SD6V08, originally featured on this system, has been superseded by the bigger compressor for some reason (faster pulldown maybe?).
ice-n-tropics
Posts: 111
Joined: Sat Apr 23, 2016 3:40 pm

Re: Old Delphi CVC-125 variable comp (TXV system) exhibiting a strange behaviour

Postby ice-n-tropics » Sat Mar 14, 2020 5:30 am

Compressor built in mini oil separator can be rendered ineffective by wear particles plugging the oil return hole which would increase oil circulation throughout the system but only very minor effect on cooling. An indicator of compressor wear is a dark grey lube color caused by aluminum fines.
hotrodac
Al9
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Joined: Tue Mar 10, 2020 3:26 am

Re: Old Delphi CVC-125 variable comp (TXV system) exhibiting a strange behaviour

Postby Al9 » Sat Mar 14, 2020 5:42 am

Don't know if you're referring to a problem with the older Sanden or to my newer comp, but this is a pic of my old control valve as soon as removed from the comp, and now that you mention it, yes, looks like there's some wear material on the smallest o-ring. But strangely enough, i can assure you that the filter was shiny clean. Oil looks clean too. O-rings were really thin compared to the ones that came with the replacement MCV.
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Al9
Posts: 114
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Re: Old Delphi CVC-125 variable comp (TXV system) exhibiting a strange behaviour

Postby Al9 » Sat May 16, 2020 6:36 am

Update: As the weather is becoming warmer and warmer (around 77 F ambient and increasing solar heat gain now) the system still seems to cool fine both stationary and moving, but what i've been able to notice is that it takes a relatively long time to achieve the liquid line pressure required to turn the condenser fan (cooling fan doubling as both the radiator fan and the condenser fan on this vehicle) on when AC is turned on for the first time in the day. About 10-15 seconds and that is with a idling engine (about 750 rpm). Air at vents starts getting cold only once the cooling fan turns on. Car is sun soaked and doors are opened while doing this and vent air still feels cold so i guess it's handling heat load just fine.

Subsequent AC startups (that is, turning AC off, letting the blower run on max speed for about one minute and then turning AC back on) however result in the condenser fan turning on immediately (about 1 second after compressor clutch engagement) and the vent air getting cold immediately. Which makes me think that the system builds pressure up somewhat slowly, but it still takes its time to equalize pressures (just like it's supposed to).

Also, i've just replaced the cabin air filter (old one looked dirty), and after checking AC operation i immediately noticed the TXV hissing/gurgling/sloshing noise with the blower fan on minimum and full air recirculation completely went away, as if the better airflow causes it to no longer reduce refrigerant flow to a trickle. Was still hissing/sloshing a little with the same ambient temperatures, blower fan speed, recirculation setting and the old cabin air filter still on. Evaporator operation is now completely silent in all conditions whether the condenser fan is on or off.

Running the AC enough time for the cabin to cool down and then parking the car, letting it sit for a short while and then turning AC back on, even after having ran the blower fan on full blast with AC off for a good time as suggested, still results in a noisy compressor startup and slower cooling. Gently revving the engine up momentarily makes the noise get quieter and quieter until it stops, and restores proper cooling. As if something suddenly dislodged somewhere.

At this point i'm beginning to suspect sluggish TXV operation (i.e. closes down fast enough but then takes way too much time to fully open again and starves the evaporator up; may not even show up on gauges anyway except as a destroked compressor and i've already ruled the control valve out) and would like to rule that out, but at the moment the virus thing is preventing a quality suitable spare TXV from being shipped and i'm not willing to fit a second hand one. Might end getting one with the same issues.

However i will likely change my mind if the "embargo"-like not enough flights to ship goods thing goes on for too long. I fear it might eventually completely fail fully closed and ruin the compressor with it.

As a side note, i recall it used to do this even a long time before adding the 2 ounces of PAG oil, so i'd rule out oil overcharge.
Al9
Posts: 114
Joined: Tue Mar 10, 2020 3:26 am

Re: Old Delphi CVC-125 variable comp (TXV system) exhibiting a strange behaviour

Postby Al9 » Tue Jun 16, 2020 10:37 am

Ok guys. Now i'm sure i need a new comp. 90F humid weather and Summer solar gain, and the compressor is now showing clear signs of excessive piston/cylinder wall clearance. Load upon engine becomes almost nonexistent as soon as the nearby catalytic converter has heated it up enough, and the thing becomes really loud (otherwise it's whisper quiet when the engine is cold). I'm getting 50F vent temperature in the shade with full recirculation at idle after driving around, and they go down when revving up. Even if stationary. I remember it performing way better than this in the near past. That poor little thing is now clearly on its last legs and unable to pump enough refrigerant around.

I'll be using a new Chinese made replacement that features some kind of improved design. Different clutch hub design (three metal leaves instead of a rubber ring), different housing design, different oil drain hole location, different control valve location. Still a CVC type compressor, more reminiscent of a Calsonic CSV613 however.
A brand new shaft seal and a new pulley bearing will be added insurance anyways (nobody is willing to replace them and i haven't got the tools).

Will fit a spare original TXV (the improved one with the encased shaft), a new receiver dryer and a spare hose set too.

Additional detail: the receiver dryer bolts are designed so that it can only be installed the right way. Can't be a wrongly fitted receiver dryer.

More later.

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