Trouble with AC Evap core tube clamp to expansion valve

kreibach

Veteran Member
Joined
Feb 18, 2005
Location
Wichita, KS
TDI
sold my 03 :-(
I've snapped 2 of these in half. It's the clamp that holds the evaporator core tubes to the expansion vlave. PN 1H0816831 (but has 838033B embossed on it). $53 not cheap!

The bently clearly says 71 inlbs on the 2 smaller bolts (item 13 in the diagram), and the same 71 inlbs on the big bolt on the engine side (item 24 in the diagram), which seems strange. Is that right?

I have an accurate torque wrench but apparently somehow this smashed the flange on the small tube and now it appears that I need to replace the evaporator core. I'm afraid I'm going to smash the new ones too. This didn't seem that hard to put together. What am I doing wrong?










 

UhOh

Top Post Dawg
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Dec 24, 2014
Location
PNW
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2000 & 2003 Golf GLS (2005 Mercedes E320 CDI)
Seems that the clamp isn't seated down flush. But... I'm confused as to what part this is supposed to be. Looks to me to be #10, which appears to show up BEHIND the core's tubes or in front of but behind the flaring of the tubes?

I don't recall having ever removed a part like you're showing: I've only messed with evaporators a couple times, in which case I couldn't profess to be an expert on such matters.

That said, I do know that 8 Nm is something achievable with say a screwdriver nut wrench (just a wrist twist/torque, no extended leverage torquing level). WAY too low I'd figure to break a casting like this (could any casting of any real thickness be broken with such small amount of torque)?
 

DivineChaos

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Joined
Jul 27, 2019
Location
Minnesota
TDI
mk6 jetta sportwagen tdi
I've snapped 2 of these in half. It's the clamp that holds the evaporator core tubes to the expansion vlave. PN 1H0816831 (but has 838033B embossed on it). $53 not cheap!

The bently clearly says 71 inlbs on the 2 smaller bolts (item 13 in the diagram), and the same 71 inlbs on the big bolt on the engine side (item 24 in the diagram), which seems strange. Is that right?

I have an accurate torque wrench but apparently somehow this smashed the flange on the small tube and now it appears that I need to replace the evaporator core. I'm afraid I'm going to smash the new ones too. This didn't seem that hard to put together. What am I doing wrong?










71in/lbs is correct. That's only 6ft/lbs. So not much at all. Just snug.
 

ghohouston

Veteran Member
Joined
Apr 2, 2013
Location
Lewisville, Texas
TDI
2001 Jetta Sedan TDI 5 Speed
I'd make sure you're getting it flush against the flare on both lines, as well as make sure you're getting both lines fully seated in the expansion valve.
 

kreibach

Veteran Member
Joined
Feb 18, 2005
Location
Wichita, KS
TDI
sold my 03 :-(
I agree that 71 inlbs isn't that much torque... but when I torqued them they kept going round and round, obviously (in hindsight) crushing the tube flanges, stretching the bolts, and snapping the bracket. Both times. So thus the sanity check. My consistent failure here makes me surprised to not find any mention of this by others online. I want this to not happen to me again.

Measuring (in inches) and calculating preload for comparison with the simple formula: Force=Torque/(.2xØ)
The single larger bolt is:
Ø.230 thread major dia
at 71 inlbs this is about 1543 lbs.

The 2 bolts going through the expansion valve and into the evaporator bracket are:
Ø.191 thread major dia
at 71 inlbs this is 1859 lbs. But there's 2 of them. 1859 x2 = 3718 lbs.

If we want the same force generated by the 2 bolts as the single bolt, then the goal is 1543/2=772 lbs which is achieved at about 29 inlbs.

Why would the evap side have such a high torque on these 2 bolts when clearly a smaller preload is sufficient to seal the joint on the other side? (I'm ignoring the pressure differences in the various tubes on the assumption that on average they are not that different from the evaporator side of the expansion joint to the other side... as a pair)
 

Genesis

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Feb 26, 2003
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Sevier County TN
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'03 Jetta Wagon
The only purpose of the clamp is to keep the O-ring from extruding. The purpose of the torque is to keep the bolt from backing out from vibration. That's all.
 

KrashDH

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Joined
Dec 22, 2013
Location
Washington
TDI
2002 Golf
Just out of curiosity, how do you know your torque wrench is "good"? What are you comparing it to? Has it been certified?

Also, are you torqueing the bolts lubed or dry?

There is always a safety margin built into the torque from the engineers. The simple math you're doing doesn't cover all the scenarios that need to be analyzed when looking at bolt calculations. Thread shear, elongation, tensile strength, factors of safety, gapping, bending etc are all scenarios that have to be analyzed. That being said, I have to agree with the others above. Something doesn't seem to be seating correctly. Then the bracket goes into yielding (bending) so you're never going to achieve the torque value, so you keep tightening it down. Until it fails.

I would borrow a different torque wrench and test off the vehicle to see what's going on. My vote is either on the torque wrench or how everything is assembling together.
 

kreibach

Veteran Member
Joined
Feb 18, 2005
Location
Wichita, KS
TDI
sold my 03 :-(
I totally agree that this preload calc is simplified and the result is inaccurate for design purposes. But I think it's sufficient for comparing the 1 bolt to the 2. Any more accurate calc would apply to both bolts, and one could cancel out the force and just go with geometry if you fiddled with it enough and end up with the torque to get the equal force. but yes, simplified.

I have a cheap bar style torque wrench (0 to 60 inlbs) and I counter torqued my lightly used $150 Proto J6064C torque wrench i got new 10 years ago. It's not a cert test, but they matched. I also used a fishing scale and torqued each while measuring the force and distance. Calculated the torque and compared to the setting/scale. It's close. Again, not a cert test, but it's another datapoint that's close. For a joint to fail this bad twice I would expect the torque wrench would need to be very out of spec, not just a little.

I put the bolts in dry since the manual didn't say to assemble with lube.

I was super careful the 2nd time, not wanting to screw it up and not really knowing what went wrong the first time. I swear everything was seated and assembled correctly as much as I could see back under there. I used a mirror and fiddled with it for 45 minutes putting it together multiple times, checking and rechecking. I torqued to 20, checked, torque to 30 and checked again, up to 40, then took it apart.... just to see. started over.. and so on, up till "tink" somewhere between 60 and 70 inlbs. grrr...

Seems that the clamp isn't seated down flush. But... I'm confused as to what part this is supposed to be. Looks to me to be #10, which appears to show up BEHIND the core's tubes or in front of but behind the flaring of the tubes?
yes, it's #10 in the manual. The slots in the clamp go on the firewall side of the evaporator tube flanges and the bolts pull them into the expansion valve and seat the orings. The clamp actually never touches the expansion valve, but presses on the flange. The clamp has a ridge where it touches the flange. Same is true on the single bolt clamp (which is captured on the high pressure line) on the engine side of the expansion valve, except the large side has a very small recess, but not enough for the clamp to touch the expansion valve. I don't have a good picture of it put together. Mine is still apart. This joint is not like the other joints where they do have face to face contact, such as the receiver dryer, compressor, etc. Those are the higher 11ftlb torques on the heel/toe joints.

I'm still stumped.
 

kreibach

Veteran Member
Joined
Feb 18, 2005
Location
Wichita, KS
TDI
sold my 03 :-(
Update - so to test the suitability of the lower torque I flipped the new cracked "clamp" over so that the crack would be in compression. I reassembled the joint with the 2 small bolts at 35 to 40 inlb torque. I pulled a vacuum, which held fine, so I charged the AC. It's been running fine for 2 weeks. Time will tell.
 
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