Low A/C refrigerant charge on CR MK5/6

aNUT

Vendor , w/Business number
Joined
Nov 29, 2006
Location
Boulder, Colorado
TDI
'01 TT (ALH-ish), B7 Audi gasser, '05 Golf
Look to post #5 for solution

Please help keep this thread on topic. If your reply isn't about significant refrigerant leakage on MK5/6 ('09+) TDI, don't post here.

So there's no shortage of A/C threads regarding the RCV for MK5/6; but I've seen at least a dozen of these '09+ cars with little to no 134 in the system. Like <100g when there should be 500-550g. Systems seem to be unadulterated. Typically these are cars with <100K miles on them, and while the system is nearly identical to the earlier MK5s, I have not seen any early MK5s low on refrigerant without obvious cause.

I've charged a couple of them only to have it all leak out again in short order. Now I'll be the first to admit that I'm probably not the world's greatest A/C refrigerant leak locator, but damned if I can't find anywhere suspect. I've used dye and UV, and I've bought a somewhat fancy electronic leak detector too. They're not leaking fast enough to detect with vacuum alone, or soapy water under normal operating pressures.

The forum hit results are all drowned out with owners having (a) RCV issues (b) smoked compressors (c) "dealer fixed it for free under warranty" (d) baseless, useless, fectless whining about their sweet new car.

The only TSBs I found were for (a) RCV (b) compressor "clutch" blows up (c) check pressure valve seal. Well, the pressure sender on a CR is on a long spindly aluminium tube, and when I get a 17mm on the sender all I'm doing is twisting the tube, so I didn't do that. Might as well just replace the whole line if it's gonna break when I try to replace the o-ring on the sender per TSB.

I figure before I invest in a dry nitrogen tank so I can pressure test the systems at 300psi or so and look some more, I figured I might put a feeler out to techs and owners that have experienced significant refrigerant leakage on MK5/6 TDI with common rail engine.

Please help keep this thread on topic. If your reply isn't about significant refrigerant leakage on MK5/6 ('09+) TDI, don't post here.
 
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colinstone

Veteran Member
Joined
Jul 25, 1999
Location
Oxford, England
>Well, the pressure sender on a CR is on a long spindly aluminium tube, and when I get a 17mm on the sender all I'm doing is twisting the tube, so I didn't do that.

Molegrip on tube, spanner on sensor and it will come off. WD40 first.
Clear that all joints assembled dry on build.
 

aNUT

Vendor , w/Business number
Joined
Nov 29, 2006
Location
Boulder, Colorado
TDI
'01 TT (ALH-ish), B7 Audi gasser, '05 Golf
Update - found it. Leaking from A/C compressor case, more specifically the over-pressure relief valve where it meets with the case.

Evacuated system. Pressurized system to 300psi w/ argon (because it's what I had, nitrogen would have been better due to smaller molecules). Since there's no liquid in the system, the pressure drop occurs more rapidly. It only dropped ~.5 psi/hour. Not much, but if I just recharged it, it would only be a month before it'd be back for the same issue.

After charging to operating pressure I was able to locate the leak using an ultrasonic leak detector, but even then it was faint. I used Amprobe model ULD-300.
 

maybe368

Veteran Member
Joined
Apr 30, 2014
Location
Phoenix
TDI
Happily none
Update - found it. Leaking from A/C compressor case, more specifically the over-pressure relief valve where it meets with the case.

Evacuated system. Pressurized system to 300psi w/ argon (because it's what I had, nitrogen would have been better due to smaller molecules). Since there's no liquid in the system, the pressure drop occurs more rapidly. It only dropped ~.5 psi/hour. Not much, but if I just recharged it, it would only be a month before it'd be back for the same issue.

After charging to operating pressure I was able to locate the leak using an ultrasonic leak detector, but even then it was faint. I used Amprobe model ULD-300.

I had this exact thing happen when I renewed the entire system on my Dodge Cummins. Got it all done and lost all the freon by the next morning. It turned out to be the over pressure valve on the hose manifold that bolted to the compressor. It was original and actually looked like it was part of the manifold. The valve had actually failed, but also had an O-ring that should have been replaced because I did a 134A conversion too. It is on the last page here:

http://www.dieseltruckresource.com/dev/ok-lets-renew-our-ac-system-t313221.html ...Mark
 
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gquenstedt

Veteran Member
Joined
May 26, 2006
Location
San Antonio, TX
TDI
'06, '03 x 2, '00
Update - found it. Leaking from A/C compressor case, more specifically the over-pressure relief valve where it meets with the case.

Evacuated system. Pressurized system to 300psi w/ argon (because it's what I had, nitrogen would have been better due to smaller molecules). Since there's no liquid in the system, the pressure drop occurs more rapidly. It only dropped ~.5 psi/hour. Not much, but if I just recharged it, it would only be a month before it'd be back for the same issue.

After charging to operating pressure I was able to locate the leak using an ultrasonic leak detector, but even then it was faint. I used Amprobe model ULD-300.
Excellent. What did you rig up to get the argon into the system?

What was the fix? Just new o-ring around the valve?
 

aNUT

Vendor , w/Business number
Joined
Nov 29, 2006
Location
Boulder, Colorado
TDI
'01 TT (ALH-ish), B7 Audi gasser, '05 Golf
Excellent. What did you rig up to get the argon into the system?
What was the fix? Just new o-ring around the valve?
I used the flow regulator and supply tank from my TIG. I purchased a cheap can tap from Advance, cut the can end of it off, and plumbed that to the outlet of the regulator. I filled through the low side service valve. I had an A/C manifold set monitoring the high side pressure. I opened up the flow regulator and discovered it tops out at 100psi, so I turned on the A/C for about 4 seconds before pressure was in the 300psi range.

I replaced the compressor. I'm so used to working on old, high mileage cars that I dismissed the oily residue. Upon closer inspection of the compressor off the car, there's tell-tale oil/dirt residue all over the case. Particularly from the seam where the 'plate' where the smaller of the two A/C ports is located. That might explain why the BRMs, which use an interchangeable compressor (though without the plate), doesn't dump all their charge. This car had only 47K miles on it. The rest of the motor's darn near spotless.

Seems to be more of a time issue than a miles issue; and certainly not an A/C usage issue. I'm got a couple of these mystery leak A/Cs on '09s and '10s last year, and over a dozen this year. Maybe it's the dry air here coupled with the lack of A/C usage during the winter that's causing the seal(s) to dry out and fail. While it stinks to tell someone they need a compressor, I suppose it's better than shrugging and telling them I don't know where the gas is going.
 
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