I suspect the clutch on my AC compressor has died in my 2006 CTT. The AC had been a little weaker in recent weeks (clutch slipping?) with periodic complete lack of cooling once or twice that went away after a restart. But now it's permanently not cooling.

I've checked fuses and codes with ICarScan - - all the temp sensors and servos appear to be working great. Haven't busted out the Durametric, but can/will. Everything seems fine except the compressor is not running (as verified by looking at refrigerant pressures which don't move except for heat soak gains).

The only codes I had were related to the blower motor controller. The blower controller that's in the car is a non-OEM replacement. While better than the completely dead original part it replaced, it's certainly suspect, but the fan is blowing fine and it doesn't explain the lack of compressor function. I've nonetheless bought a replacement as the current one is clearly throwing codes, and replacing the controller is relatively easy/cheap.

Assuming the blower motor controller is not my issue, any tips on how to test the clutch or what else to check? It's very tight in the engine compartment down by the compressor, so appreciate advice on testing procedure.

And, has anyone replaced a compressor? I've got all the gauges, vacuum pump, etc. There's not much online I could find on this topic, but from what I read it doesn't seem impossible. Looks like the job gets bigger once you factor all the "while you are in there stuff": serp belt, pulleys, water pump, charge pipe o-rings, etc.

Appreciate the thoughts.

 

Is there a enough refrigerant pressure for the A/C compressor to kick in? If there is a leak and not enough pressure, then the compressor won't kick in.
Before paying big bucks for A/C parts, have it checked by a reputable professional.

 

i recommend you to check for leaking. i had same simptoms on my 2006 CTTS and when a/c stop cooling we test it for vacuum leaking and this was the problem.

 

There are a few possibilities. Others have already mentioned leaks and low refrigerant charge. What you have described is also fairly typical for a malfunctioning compressor control valve (CCV). You might want to read this thread: https://rennlist.com/forums/cayenne-...-location.html

 

Refrigerant charges are good. I'd added a some 134a a few weeks back, but it didn't need much. There was an overpressure code logged when I most recently checked, but that has since been cleared, not to return. I also thought maybe I over charged it, and took some gas out, but it's made no difference.

Brett, thanks for the compressor control valve lead. Will check that out.

This post in the thread you linked sounds identical to my situation:

https://rennlist.com/forums/cayenne-...l#post16016700

 

I think the CCV accumulates some gunk over time and gets sticky. I wouldn't be surprised if just cleaning the valve fixes the problem, but the valves are cheap. No doubt that many perfectly good compressors are swapped out when all they need is a CCV. If you swap out the CCV, be sure to pull a really good vacuum on the system before recharging and replace the drier while you are at it for good measure.

 

I've got to thank brett968 because that thread lead me to replace the CCV recently and revive the A/C in my 2004 CS; I really appreciate the information there.
Since I got the car the temperature would never go anything below mildly cold and I needed to keep the blower at the highest setting in hot days but after replacing the CCV the A/C is blowing nice cold air with temperatures at around 107 degrees F, therefore I would agree in checking for leaks then go for the CCV.
Also if recall correctly there is no clutch in the Cayenne's compressor right?

 

Thanks again to Brett968 for the steer to look at the CCV -- that valve (and/or the wiring to it) does seem VERY suspect at this time. I remember having to struggle with the wire to that valve when I replace my valve cover gaskets -- hope I didn't create a situation where something melted/shorted out.

One question for the CCV experts -- should I be seeing any pressure signature on the H/L side ports with the engine [and compressor] running?

I'm basically seeing just a system pressure (100+psi depending on ambient/engine temp) -- it's maybe slightly higher on the high side than the low side. As the engine bay heat soaks, both low and high side pressures increase to maybe 150psi (it's super hot in Houston right now so those pressures don't strike me as odd overall)

I don't know how the CCV works, so maybe it's stuck in a position that's essentially bypassing my compressor (assuming it's working)? Appreciate any additional thoughts.

Also, some information for posterity sake:
- It appears the 955 Cayennes use the Denso 7SEU17C compressor (with 7 groove pulley) -- Note that from what I can tell, you can't just buy any 7SEU17C compressor, as they have different pulley configurations/alignments depending on application. [SUBSEQUENT NOTE: SEE MY FOLLOWUP POST BELOW WITH THE SPECIFIC PART NUMBER THAT WORKS FOR THE 955 v8 CAYENNES]
- Per Google searches, it appears that the 7SEU17C compressor does NOT use an electro-magnetic clutch but rather a shock absorbing clutch/dampened pulley arrangement. I base that statement on pictures of the compressor which show no electrical connection.
- Based on the above, and Brett968's prior experience, it appears the CCV (otherwise known as the compressor solenoid) does the regulating of the compressor function. Brett had success replacing his CCV with a part called "Gogoal ECV03C". That part appears to be sold out/on backorder. But this one appears similar (and available): - Ebay also has some other CCV's -- you can find them by searching for 7SEU17C and looking for the control valves that have the wire pigtail included. There's another style that doesn't have any cabling -- that's not the right one.

One last question: Any tips on where to access the receiver/dryer? It appears to use a replaceable element rather than an entirely new part?

 

It sounds like there is no refrigerant flow. High side pressure should be significantly higher than low side when refrigerant is flowing. I don't recall the exact numbers (and they vary with ambient conditions) but I would expect around 180-200psi high side and 20-40 psi low side when the system is running properly.

These cars use variable displacement compressors. Basically, the CCV takes an electrical signal and commands the refrigerant flow through by controlling the position of the variable displacement mechanism. Your idea about the valve being stuck is accurate.

Correct, there is no electro-magnetic clutch. The damped pulley is also designed to break away if the compressor seizes so that the belt doesn't break.

The main difference between the variants from what I could tell was the connectors. It sounds like you already figured this out. I would say that the valve that you linked to has a good chance of being the correct one.

Quote:

One last question: Any tips on where to access the receiver/dryer? It appears to use a replaceable element rather than an entirely new part?

There is an access port in the front bumper core support. With the hood open and looking down at the core support, it is on the passengers side and should have an ~1.5" rubber cover over it (which is likely missing). The drier is removed by pulling it out vertically. It is held in by a circlip.

 

Thank you!

Parts have been ordered. Going to do the serpentine belt, pulleys, and water pump while I'm in there....

Will report back in a couple weeks.

 

So that's what that round hole is for... Been wondering about it since day one.

 

I had a problem with a compressor on a 955 2005 3.2, but I found a good indy to repair it. The cost was around 200$ instead of 400$ plus oil, freon, labour etc that should have reached around 500$ or more.

The compressor itself was in good shape after 15 years with almost perfect clean oil, but the valve from it failed so it had to be replaced with a new one that costed around 80$. The rest up to 200$ was labour, freon, new oil for compressor etc.

What happened when the compressor was not working was that it was pumping just hot air or sometimes was pumping cold on one site and hot on passenger's side and on restart it was all over hot air again. I believe that a good service specialised in compressors can deal with the problem.

 

So it turns out my compressor is locked up. Post mortem suggests that I was likely low in oil in the system - - none dripped out of the compressor. The good news is that the oil in the lines looks yellow/clear and not burned/black.

And as discussed, the compressor pulley has a one-time mechanical "fuse" - - see attached image. The pulley actually spins freely on the compressor, and when functioning correctly, drives the black metal drive hub on the end that's kind of octagonal/multi-pointed star shape. There are ramps between the pulley and black drive hub, and if the compressor seizes, the ramps force the drive hub to bend away from the pulley so that the pulley can still spin and not break the belt.

Other info: the AC compressor is on the bottom of the engine on the driver's side. An easy check to see if your compressor is seized is to see if the black drive hub on the end of the pulley is flared outwards -- there are 4 "petals" or quadrants that will be and flared out away from the pulley (see my picture). Wish I'd known, as it would have saved time ordering parts (and not ordering a new CCV) .

The correct replacement compressor for the V8 955/957s is pn 948.162.011.01 which is essentially a Denso 471-1326. I've got a Denso on order for less than $400 delivered with tax. The bigger cost is the labor.

Removing the compressor isn't terrible with the right tools, mostly torx and reverse torx sockets, but in my case I had already removed the fan shroud as I was also replacing all the drive belt pulleys and water pump on the front of the engine (which I strongly recommend while you are in there). That necessitates removing the boost pipes, Y-pipe, air filter housings, and throttle body. It's a good amount of work, but opens up a lot of space between the radiator and front of the engine. I'm not sure the compressor would have fit out the bottom of the engine without doing all that prep. Maybe. But it was pretty tight under there.

Also, I can confirm that this Compressor Control Valve (CCV) is the same size and cable length as on the V8 Cayennes: https://www.ebay.com/itm/NEW-A-C-Com...0-a9ae669b43e0
Although it's been said on a forum somewhere that it's possible to replace the CCV with the compressor installed, I'm not so sure it's that easy. it may indeed be possible, but it's likely very challenging and/or requires small hands with a vice-like grip...

Hope to get it put back together next weekend. New compressor and more AC supplies (orings, expansion valve, line flush, etc) have all been ordered. Got the water pump and pulleys installed today. Just need to flush lines, install compressor and expansion valve and new dryer, pull a deep vacuum, and recharge with 700g of 134a.

 

OK, so update after a long [holiday?] weekend:

1) New water pump installed
2) New belt, pulleys and belt tensioner
3) New vacuum hose to diverter valves (I found a huge vacuum leak!!!), but cleaned and reinstalled the original diverter valves (NOTE: Vaico diverter valves are garbage -- both valves leaked pressure as new. Not sure whether they break-in, but I'd rather just send them back.)
4) Lots of cleaning, degreasing, reconditioning and refitting of the boost pipes and associated o-rings and hardware
5) Multiple reverse flushes of the evaporator, low-side lines, and condenser and high-side lines; Looked pretty clean; oil was grayish, but not filthy or glittery. Pulled a long vacuum on the system: It took 18 hours, but I got down to 300 microns, with holding mid 400's after a 10+ minute rest period.
6) New AC compressor, new drier element, but had to use the old expansion valve... -- I bought a new expansion valve, but there was a change mid-year in 2006, and I bought the wrong one. Argh....
7) Added two and one-half cans of 134a -- worked out to about 800g, so overfilled by 50g. Note: Required putting cans in near-boiling water to continue charging the system after the 1st can.
8) Disassembled old compressor and did post mortem: More carnage inside the compressor than I'd expected to see given how clean the lines were. I think the compressor was i) low on oil (there was surprisingly little in side -- almost none dripped out), and ii) likely overcharged [by me] which resulted in too much pressure breaking down one or more of the bearings on the swash plate. Once those bearings go, the compressor is done in very short order. Interestingly, I noted some corrosion on some of the reed valve plates. Moisture in the old system?

Results:
- Belt drive and water pump sounds great, i.e., super quiet.
- Car drives great -- vacuum leaks really ruin the driveabilty of the CTTs. I can't believe how much difference $5 of rubber hose can make. Totally smooths out the part-throttle engagement
- And the AC initially didn't work.... Turned out I needed to reset the codes (pressure low) on the system. Once I did that, the compressor magically fired up (and by fired up, I mean it showed differential pressure on the high/low sides -- otherwise they'd just more or less match)
- But with the AC working and showing good looking pressures at idle (80-85F ambient: low ~40psi / high ~190psi), I'm getting only "cool" air, not the Arctic Freeze Ray I know the system is capable of. But at least it's consistently cool -- cool enough to live with for now -- it will get the car to livable temperatures, just not as fast as I know it once did. Why?

Using iCarScan x431 I've confirmed the following:
- All vents/dampers fully operational, including mixing flap -- this is confirmed by looking at the min/max swing on servos on the app -- I've not had actual eyes on the mixing flap in operation to confirm. I'm still a bit suspicious of the mixing flap.
- Ambient air temp: ~90F / 32C
- Typical inlet air temp: 35C
- Typical evaporator temp: 12-14C -- this seems high to me by about 10C
- Vent temps: 14-16C -- Again, seems high by about 10C
- Cabin temps (in direct sun): ~25C (77F)
- System reads AC pressure of 15-16bar in operation (~220-235psi implies ~85F high side pressure, a smidge low for the ambient of ~90F)
- Interior fan speeds are staying high for a given temperature -- suggesting the AC computer knows it's not cool enough and is moving more air to compensate?

Possible issues preventing max cool:
- Condenser clogged? Saw no evidence in the old drier or while back flushing. No glitter, no issue flushing or moving air through.
- Condenser fan died? Not sure -- at least one fan is working, but there are two. Didn't test, but seems possible. Need to see if I can operate the fans individually with the iCarScan app. Not sure where that feature would be. It's not in the HVAC section. Will look.
- Expansion valve is kaput? I did reuse the old one (I gave it a thorough clean/spray). This would see very logical, but I'm confused by the good looking pressures on the compressor. Can system pressures look right, but the TXV doesn't let the right amount of refrigerant through, thus limiting cooling?
- Evaporator temp sensor? Easy to test, but the common temps between the evaporator and vents would see to suggest that they're all reading correctly. For $10, I've bought a new one and will install.
- Inlet air temp sensor? From what I've read, this can fail causing the compressor to not come on (if the value is less than 5C), but I'm getting correct looking readings and the compressor is running, so don't think that's it.
- Air Quality Sensor: From what I can tell, this only affects air recirculation function. AC runs the same with it unplugged.

Would love any thoughts on how to get "Ice Cold Freeze Ray" performance back....

Will post pictures later.


.

 

Providing an update on this. The AC is definitely working, but isn't 100% right.

Some times the evaporator temp will be 3C (freeze ray), other times it's like 15C (meh). And the swing in temps will happen even under steady-state highway driving conditions -- so I don't think it's a condenser issue.

I believe the temps as reported by iCarScan, as they match the vent temps within a couple degrees -- It does not appear to be a sensor issue and the pressures look good.

If I hadn't just filled the system by weight, I'd guess that I was a smidgen low on refrigerant. But I think in this case, I likely have a sticking/unreliable expansion valve which is periodically not metering enough refrigerant through the evaporator (and hence it occasionally gets too warm).

Honestly, it seems to be working well enough -- I may leave it as is for now. Or maybe I'll recover the refrigerant, change out the TXV, and give it another recharge -- not including pulling a vacuum, I could probably do that in an hour or two at this point. We'll see...