AC Compressor vs. RCV

[Stealth TDI]

Hello,

I had a weird problem with my AC. It works great. Only during this long road trip has it given me any trouble. It gets a little warm after about two hours of driving. It's about time for a break by then, so I stopped. After about 15 minutes (duration of stop seems irrelevant), we got back on the road and all is well, with my face being frozen, the AC is great once more... for another 2-3 hours. WTH? Looking back, I have had other very brief losses of AC before. I assumed they were brief events during (what shouldn't be) normal car functions.

So my requisite search here at TDIClub revealed that this is a very common problem in Mk5s and Mk6's. I must admit that it's frustrating because, just when I thought I was "drive more worry less" about the HPFP, now I get to deal with this AC crap? Really? On a 15-month old car? And I'm not alone? Not even close?

The car has 34,000 miles on it. The 36k warranty is almost up. A visit to the dealer will likely produce an "unable to replicate fault" diagnosis. Shall I try anyway? Is the issue common enough for VW to recognize? I feel it should at least be documented prior to warranty expiration in case they refuse service now and I opt to take it back later.

Once the car is out of warranty (assuming it will fail again), I will pursue the RCV replacement and just be pissed every time I have to have hours sucked out of my life to drop off the car for repair. This is a real drag, especially knowing that my Mk3 still has its original compressor.

I appreciate your thoughts.

Scott

 

[993er]

The car has 34,000 miles on it. The 36k warranty is almost up. A visit to the dealer will likely produce an "unable to replicate fault" diagnosis.

Have your complaint noted on a work order and get a copy for future reference.

 

[Stealth TDI]

Thanks for the note! I'm inclined to visit the dealer just for that reason. However, I'm not convinced it'll help much. Odds are good that I'd try an RCV swap before trying to have the dealer swap out the entire compressor. I feel like something else will go wrong the deeper they dig. My car is at 35,100 miles now. So I need to act quickly. I usually drive ~500 miles per week.

 

[VeeDubTDI]

Are you losing airflow and cooling, or just cooling? If you're also losing airflow, then your evaporator could be freezing up.

 

[Stealth TDI]

YES! I am losing airflow. I thought I was imagining it. Does that mean something else?

 

[j-bone]

YES! I am losing airflow. I thought I was imagining it. Does that mean something else?

This might be a normal cycle as weird as it sounds , if it's what veedubtdi is explaining. It might go into a defrost " mode " But I'm no expert in this field . I took a 3 hr trip with the a/c on low and never had a problem.

 

[Scoutx]

Hmmm.. I might want to consider an icing problem in the evaporator. Over long periods ice builds up, blocks airflow which compounds the issue.

When you stop ice melts until system runs long enough to ice up again.

If this is the case a short solution would be to simply turn off the A/C for a few minutes every hour and let the air flow melt the ice. You shouldn't notice any real difference in cooling since the ice will continue to supply cold air until it's gone.

Long solution may be that your compressor has it's variable displacement misadjusted and/or refrigerant level is wrong.

Certainly take it in and get it noted for possible future action.

 

[Stealth TDI]

Hello,

I felt the "cycle" was normal when it lasted for just 15-30 seconds. But 15-30 minutes is no good, especially when it's over 100 degrees outside! One of my (bad?) AC habits is to set it to max AC and then point the vents away from me. I prefer cold air around me instead of blowing right at me. Perhaps that's not a good thing even though I leave the fan on #3 for more airflow across the coils.

Perhaps pointing the vent at me and then blending-in some heat would be better and prevent icing? Thoughts?

I'm glad to know that my current issue may not be the RCV. Those brief stops may have been what was needed to melt some ice and "fix" my problem for a while. But I'm still annoyed to know that the RCV is a common problem and has been for many years. C'mon, VW, FIX IT!

 

[VeeDubTDI]

YES! I am losing airflow. I thought I was imagining it. Does that mean something else?

If you're losing airflow, then your evaporator is freezing up, resulting in no cooling and reduced air flow. Your refrigerant charge level may be too low.

 

[VeeDubTDI]

Hello,

I felt the "cycle" was normal when it lasted for just 15-30 seconds. But 15-30 minutes is no good, especially when it's over 100 degrees outside! One of my (bad?) AC habits is to set it to max AC and then point the vents away from me. I prefer cold air around me instead of blowing right at me. Perhaps that's not a good thing even though I leave the fan on #3 for more airflow across the coils.

Perhaps pointing the vent at me and then blending-in some heat would be better and prevent icing? Thoughts?

I'm glad to know that my current issue may not be the RCV. Those brief stops may have been what was needed to melt some ice and "fix" my problem for a while. But I'm still annoyed to know that the RCV is a common problem and has been for many years. C'mon, VW, FIX IT!

Heat is added after the evaporator, so adding heat probably won't help with the evap icing.

 

[Stealth TDI]

Hmmm... Good to know. I've also read somewhere that icing can occur if the refrigerant is low. I suspect this needs to go to the dealer for documentation (in case of a leak) and/or to fill the AC to specs in case it was low from the factory.

PS: HAHA! I just saw your other post, Lawson!

 

[Aztraveler]

I had the same issue with my 2014. Had it checked by dealer. Twice. Classic "no problem found." I too was approaching 36k miles. I responded negatively to my service survey and I was contacted by the service manager.

He rescheduled a service appointment to check out the AC.

I had to go out of town for a family emergency. I crossed the 36k mark during my return trip.

Rescheduled for after my return. It happened to be a 100 degree day. They found it was low on freon. They evacuated and recharged. Worked great after that. We've had a hot summer this year.

I haven't been able to drive it in about a month. During another trip, this time for a funeral, I was t boned by car running red light. Caught me in the left quarter panel and axel. About 11k in damage.

It is scheduled to be done on 8/21. And I am back in MI for another family emergency.

When I get it home I will do my 40k service. Already have everything I need.

Sent from my SCH-I605 using Tapatalk

 

[VeeDubTDI]

I think you'll find that the dealer will either not be able to replicate the problem or they will tell you that refrigerant loss is considered a "wear item" or "normal" and that they'll have to charge you for a complete system evac/charge.

Take it to a shop you trust and have them evacuate the system and recharge it by weight. You can't really diagnose or fill these things with traditional gauges because of the RCV varying the load on the compressor.

If the problems persist after a proper charge is verified, then you'll need to move down the troubleshooting tree. It could be that your RCV is getting stuck in the higher load position, making it unable to unload the compressor when the evaporator gets too cold.

 

[Jonathan-]

Do these A/C systems in these cars not have a freeze switch? Most systems have a switch to shut the compressor off when it starts to freeze up, before you would start to notice any drop in airflow. I know this isn't the root of the problem but it should keep it from freezing completely I would think.

 

[VeeDubTDI]

Actually, first things first. Hook up VCDS and go for a drive with the A/C set for your usual settings. Monitor the compressor load and the evaporator temperature in the HVAC controller. You shouldn't see evap temp go below freezing, and the compressor should unload as it approaches the minimum evap temp or the cabin approaches setpoint. Try varying the fan speed and temperature sensors and watch the results, as well.

This is assuming that you have an HVAC controller that can communicate with VCDS. I don't know how smart the non-Climatronic cars are, as I've never messed with one. Hook it up and let's see what you find.

 

[compu_85]

There's no freeze switch, but there is a temp sensor on the evaporator.

However, with the variable displacement compressor it should never be able to cool below freezing even if the computers freak out and call for 100% cooling... it should self regulate just like the mk3 and mk4 cars.

-J

 

[Stealth TDI]

Okay. I checked the module in VCDS and saw the following:

As you can see, the car had been sitting for about eight minutes by the time I had snapped all three shots. But I did this after a 45-minute drive on Max AC and recirc. If anything was frozen, I don't think it would have thawed unless the reduced airflow across the radiator had an effect.

Thoughts?

 

[VeeDubTDI]

So that looks pretty good... your compressor current is .71 (.85 is full load), so it has unloaded a bit. I think "temperature behind condenser" is mislabeled and it's actually evap temp, but I'm not certain. Does this go up to ambient when you turn off the a/c?

 

[Stealth TDI]

I'll check that temperature reading during my drive tomorrow.

 

[Stealth TDI]

Okay. I pulled some data this morning:

Cold start and idle, no AC...

On the highway, no AC...

On the highway with AC on for a few minutes...

After AC had been running for about 15 minutes...

After AC had been running for about 30 minutes...

It sure looks like everything is working. The condenser temp actually dropped to 0 degrees at some point. But it didn't stay there for long. It was only 77 degrees outside. So the cabin got quite cool and I could see that the compressor current was dropping, perhaps since the RCV was dialing back pressure to maintain ~2 degrees of condenser temp?

I think it'll be a while before I'll take another 3-hour trip in the kind of heat that'll freeze up my condenser again. I guess I'll consider my issue to be a non-issue and remember to turn off the AC and let it thaw if I feel a loss of cooling and airflow in the future.

Thanks for the lessons, everyone!

Scott

 

[07ktm250xc]

veedubtdi is right..that "condenser" temp must be the evaporator temp. The condenser discharges heat.

 

[NAZ TDI]

Have you changed the cabin air filter? If plugged it will restrict air flow. If the evaporator really is freezing (from moisture in the air) there is something wrong in the system that needs to be addressed. It's very unlikely that low refrigerant would cause evaporator freezing! When the refrigerant is low, pressures drop and the system cannot get cold enough to freeze the moisture out of the incoming air. Instead, it just blows warm. Odds are it is the RCV.

 

[VeeDubTDI]

veedubtdi is right..that "condenser" temp must be the evaporator temp. The condenser discharges heat.

Yep - the label file in VCDS is incorrect. It should be temp behind (downstream of) evaporator, not temp behind condenser.

Everything appears to be working well - the compressor unloads (lower compressor current) as evap temp approaches freezing. If it stays at 0C for too long, it will start to ice up - so pay particular attention to that the next time you're logging data.

Checking/changing the cabin air filter is a good suggestion.

Low charge (to a certain extent) can absolutely cause evaporator freezing. There is, of course, a point of diminishing returns when a charge blow a certain level will result in reduced system performance. Don't rule that out.

 

[meerschm]

Okay. I checked the module in VCDS and saw the following:

As you can see, the car had been sitting for about eight minutes by the time I had snapped all three shots. But I did this after a 45-minute drive on Max AC and recirc. If anything was frozen, I don't think it would have thawed unless the reduced airflow across the radiator had an effect.

Thoughts?

I want to know how you got so many measuring blocks in the window.

 

[Stealth TDI]

LOL!

I want to know how you got so many measuring blocks in the window.

Corel PhotoPaint and some time.

 

[compu_85]

Here's a quickie way to see if the charge level is ok: With the AC running, the fan on high, and a hot day the (large) suction line cold where it goes into the compressor should be cold after the AC runs for a short while. If it isn't the charge is probably low.

-J