I have a leak on the expansion valve of my 420 sel. The leak is not at one of the four pipes transporting the refrigerant. It is at the fifth opening or plug or cap or whatever it is. I assume it is to adjust flow. At any rate, is there a seal that I can re fit into this port or must I buy a new Valve. Removal of this valve requires special tools and a good back. I have neither. If I buy a new valve and tools, and manage the job OK, is there any one who knows if this is an adjustment and how to adjust it???
The system is R12 and I have plenty. About 200 lbs. I am a licensed refrigeration person (not in the mobile field) and must repair leaks, I cannot just keep dumping in R 12.
Ron

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I love my Mercedes

That portion of the expansion valve is not servicable. You will have to replace it to fix the leak. I'm not familiar with your chassis. I am assuming that it is under the dash since you are hesitant to replace it.

If you can see it to determine that it is leaking I would think that it wouldn't be a terribly bad job to replace, but of course, I haven't seen it to know what you're faced with.

Sorry to be the bearer of bad news.

Good luck,

Ron,
You have 200 lbs. of R12? MY NEW BEST FRIEND!

You are correct on the need for a strong back and crowsfoot flare wrenches to remove the expansion valve. Some have done it with "stubbies", but not me. Emphasis on the flexible back

Since you are a pro tech on large supermarket systems, you'll know more about this than I do, but I happen to have an expansion valve in my hand as I type this and have disassembled it numerous times, so I'll tell you what I've found (FWIW) : the brass plug is adjustable to open or reduce flow in the TXV valve (nothing different from the old Chrysler H block style) although Mercedes gives NO info to users or techs on this fact. It uses a ball and spring on an orifice seat, spring tension adjusted by screwing in (or out) the brass plug. Just stick a nail set or small drift in the eccentic hole and twirl. The plug DOES have an "O" ring (looks like a standard 1/2", but probably a 12mm.) You'll undoubtably have it's equivalent in your parts bin. Mark the plug and block before unscrewing it, so you get the correct tension when replacing, and don't lose the little ball! Good luck

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

When we first started retro-fitting MBs to 134a we used to close up the valve using that adjustment. Then they started selling 134a valves and it wasn't necessary. Now I resist retrofitting like the plague.

For almost all uses I would rather swap the valve than fix it. No matter the reason for removal we never reuse an old valve they are just too cheap and too important. That late 126 body has to have the worst access of any MB TXV. They are resealable though as I have been into many of them.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

I thank you ALL for the help. I don't have the wrenches I need. So before buying them and trying the job of replacement, I think I will try to remove the end and fit a new o ring. This is no easy task. Very good possibility I will not be able to reassemble in place. But the most I can do is ruin the valve.

It is strange that the replacement valve did not ask which gas was in the system. I went to several suppliers on line. Be that the case then instructions on adjustment should accompany valve. ( One would think)

I was also torn with the thought of retrofitting to r134a as long as I am faced with replacing the Valve. But I have certainly read enough articles about trouble that exists with retrofit. I know on a personal level, at work we had many leaks develope after retrofit. Two reasons were named. one was the fact that the oil is a great cleaner, the other was that the mixing of the two oils caused a reaction on the o rings. This proved somewat true in newer intalls with same gas. No leaks occurred at all for years.
Well,
Thanks again,
Ron

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I love my Mercedes

Refer man,

Yes it is strange. The 134 TXV has been available for some time. I suppose if you are buying a direct replacement, you are getting an R12 unit. If you were to click on Parts Shop above and contact Phil, I'm sure he could clarify this for you.

I know that I am "preaching to the choir" about 134 conversion, but in converting most MB's you run into more problems than possible leaks. As you know, you lose about 15% of your cooling capacity when going to 134 with no other changes. Most of the MB a/c systems of the seventies and eighties, and even into the mid nineties on some models, there is just no extra margin of cooling capacity as many other cars have.

Since you have plenty of R12 I think that fixing your existing TXV and recharging with R12 will give you the most satisfactory system.

Good luck,

Since i am still trying to find a freon leak, this valve may be a possible candidate. There is dye in the system.My question is, [where is this TVX valve].

420 Benz,

It is under the dash on the drivers side prety much up against firewall.
If you are using an electronic leak detector, it should pick up the leak just by sticking it up there in that area.

Ron

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I love my Mercedes

REFER MAN: I am using a blue lite. Is it sisible enough to see with a lite?

Yes,
It is directly above the edge of the tranny hump. But ir is wrapped in insulation. But mine was visibly dripping oil everything in the area under it was oil soaked.
If you follow the refrig lines thur the firewall, they go directly to the valve.
Ron

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I love my Mercedes

tHANKS: Refer Man for the info.

I removed the adjustment cap being careful not to drop the spring and ball (both remained in place luckily). I took the cap to my local MB dealer. He could not match the Oring with a MB part. But we did find a Volvo Oring that looked exact. And it was for the AC system, so I was confident it was of the correct material. I put it on the cap, oiled it with refrigerant oil and assembled. It went much easier than I had expected, which of course worried me because it could not possibly have been tight enough to seal. But so far it appears OK. I leak tested, evacuated over night and put just enough gas in to bring the pressures to possitive numbers.

When I finished work I went home and leak checked again. Found a leak at the compressor seal. I gassed it up amyway to make sure the expansion valve worked. It did. I leak checked again and this time no leak anywhere.. This car doesn't get used much. Maybe running it lubed up the seal and it will be OK for the season. Then next year I will attack the compressor.

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I love my Mercedes