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#1
03-20-2006, 07:15 PM
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Stripped threads on evaporator line
1990 Mercedes 300SE
Engine 103.981 Chassis 126.024 I was replacing the a/c expansion valve and I overtightened one of the lines coming from the a/c evaporator going into the expansion valve. As a result the top two threads of the evaporator line fitting are a little flattened on one side. There was a definite leak at that line when I pressurized the system. I had a friend suggest that I try a combination of teflon tape AND blue loctite on the fitting threads to "seal" the flattened threads. I wanted to get some other opinions before I try this. Any suggestions will be greatly appreciated and, yes, I know now to be very gentle when tightening down copper fittings  )Michael C. 
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#2
03-20-2006, 08:12 PM
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I doubt very much that minor thread damage is causing your leak. Either you've got O-ring problems, or the thread damage is greater than you've said.
__________________
1989 300 SEL that mostly works, but needs TLC
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#3
03-21-2006, 09:11 AM
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The O-ring seals the line(s) to the expansion valve..unless the o-ring ISN'T against the expansion valve due to thread damage. Have you tried a thread file?
__________________
MERCEDES Benz Master Guild Technician (6 TIMES) ASE Master Technician Mercedes Benz Star Technician (2 times) 44 years foreign automotive repair 27 Years M.B. Shop foreman (dealer) MB technical information Specialist (15 years) 190E 2.3 16V ITS SCCA race car (sold) 1986 190E 2.3 16V 2.5 (sold) Retired Moderator
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#4
03-21-2006, 09:39 AM
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Can you post a photo?
The only fastners that hold the expansion valve to the evaporator are two 3 mm hex head bolts that are recessed in the expansion valve and screw into a plate that goes behind and around the two pipes that come out of the evap.
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#5
03-21-2006, 12:32 PM
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No, I have not tried a thread file.
A little more info and a photo: When I removed the lines from the expansion valve after the failed pressure test, I neglected to mention that the line I overtightened was loose. When I say I overtightened it, what really happened is the fitting "spun" a little on my last turn of the wrench. I knew I had screwed it up but did the pressure test anyway. Thanks for the quick responses! I hope the photo helps. P.S. I know the O-Rings for the evaporator lines are missing in the photo, they were properly installed when we did the pressure test. Here is the photo: (Red arrow points to damaged threads)
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#6
03-21-2006, 12:40 PM
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That is a different setup from the way the lines connect to the expansion valve on the three 124's I've dealt with.
The fix. Would it be possible to run the proper size die over the damaged threads? It that lip on the tubing does not interfere I'd try that. Edited: You probably know this now but with those flare type fittings, if you can not screw them in a good ways to start with your fingers don't even think about tightening them with a wrench, because they are not going to go on straight.
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#7
03-21-2006, 12:43 PM
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Oh I understand now. Sealing the threads isn't really the problem, I have to REPAIR the threads so I can get the fitting to screw all the way down and get tight. I guess that is why M.B. Doc asked if I had tried a thread file.
Can a die be used to rethread this copper fitting? If not, I will try the thread file. Thanks again everybody.
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