Stripped threads on evaporator line - PeachParts Mercedes-Benz Forum

Beach_Benz · #1 03-20-2006, 06:15 PM

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.

Moneypit SEL · #2 03-20-2006, 07:12 PM

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.

mbdoc · #3 03-21-2006, 08:11 AM

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?

Ron in SC · #4 03-21-2006, 08:39 AM

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.

Beach_Benz · #5 03-21-2006, 11:32 AM

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)

Ron in SC · #6 03-21-2006, 11:40 AM

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.

Beach_Benz · #7 03-21-2006, 11:43 AM

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.

Beach_Benz · #8 03-21-2006, 11:46 AM

Sorry Ron, you replied so fast I didn't see you mentioned a die yourself.
I did run the fittings down by hand before putting the wrench on them but I guess I just got a little overzealous on that one line.

Ron in SC · #9 03-21-2006, 11:47 AM

Quote:

Can a die be used to rethread this copper fitting?

That fitting appears from the photo to be brass.

Beach_Benz · #10 03-21-2006, 11:54 AM

Right you are, Ron, it is brass.

Ron in SC · #11 03-21-2006, 11:58 AM

It occurred to me that maybe the hole in the evaporator that the fitting screws into is messed up. Could that be? Might want to run a die in that too. But filings may fall into the hole, if that's the case maybe a new expansion valve.

Beach_Benz · #12 03-21-2006, 03:57 PM

The threads inside the expansion valve seem to be OK. I guess I will try to find a die that will work and try to fix the threads on the evaporator line this weekend.

Mike Murrell · #13 03-21-2006, 05:55 PM

I had a similar problem once with the low side service line on my Benz's R-12 compressor. A thread die cleaned it up so that I was once again able to coonect the low side manifold line.

Won't hurt to try.

jbaj007 · #14 03-21-2006, 10:42 PM

A little pricey, but maybe someone has it to loan?

http://www.acsource.com/index.asp?PageAction=VIEWPROD&ProdID=603

Beach_Benz · #15 03-22-2006, 09:18 AM

Thanks for that link! I ordered the correct thread die yesterday from Napa; it should be in today. I will probably try it out today and hopefully post the results tomorrow or friday.