Can you just use O-rings from a hardware store?
 

I was wanting to replace all the O-rings in my A/C system lines. Instead of trying to order them from the dealer or auto parts store could I just match up a set from the hardware store? They look the same but are way less.
Anyone do this with satisfactory results?

No, don't even think about it.

What about generic ones in the auto parts store?

If they are A/C o-rings, they should be fine. There is nothing "special" about the A/C system on a W123.

I bought an assortment for European cars that included everything to reseal my entire system for under $6. And I still had half the assortment left over.

Here you are:
http://www.ackits.com/merchant.mvc?Screen=PROD&Store_Code=01&Product_Code=CP3025&Category_Code=vehiclespecific

That's the reason I was wondering since I was thinking the same thing that there is nothing special about the A/C system.

My local hardware is very good.

But they don't carry metric o-rings.

I think the difference between metric and SAE wouldn't be that much of a problem here.

Get the proper seals from the dealer. Why cheap out on something that is as difficult to change as A/C seals? The green ones that they will sell you are good for R12 or R134a.

What is it about an a/c seal that it needs to come from the dealer? Does a Mercedes use a different refrigerant or oil than any other car? Do you need to make sure that you only buy "Mercedes" R-12?

I don't have any idea what the dealer would charge for them but I was thinking it would be many times more than what I could find in a hardware store. Also my closest dealer is an hour away.
A/C seals are A/C seals. Also the compressor is the same model used in GM cars so I see no need to look specifically for MB parts here.

Agreed. But hardware o-rings are typically for plumbing applications. But if your hardware store sells automotive A/C seals, that's great. If they don't, just about any auto parts store should be able to fix you up.

You've got to have some sort of auto store near you....the A/C seals they sell will be better suited to the job than those from a hardware store....

I've picked up a couple of variety packs of nitrile AC system seals at places like Schuck's and Autozone in the past. They're metric, of course. A $5 packs gives you enough to do the entire system on most cars with some left over. I've had no trouble with them at all in either R-12 or R-134a systems.

That sounds like a cheap and easy way to go.

One way, not the other...
 

I'm ramping up to convert back Gray Ghost to R-12. In doing research it seems hoses and O-rings are different for each due to the molecular structure of each refrigerant. R-12 has fat molecules; R-134a's are smaller in diameter and, in a cheaply converted system, can leak through the OEM seals and hoses. That's why some references reccomend using "barrier" hoses as the molecular make up is less permeable.

In summary (I think) OEM hoses and original rubber O-rings (usually black) are OK for R-12 but will leak R-134a. Barrier hoses and the green metric O-rings, since they are designed for the smaller R134a molecules, will also work for R-12.

Recommend Diesel Giant's photo essay on DIY AC system purge. In it he recommends getting the O-rings from NAPA (just take in all the old and match them up) and to dip each ring in that special AC system lube oil.

Good luck.

I was planning on maintaining the old R12 system since the outcome will be more predictable. Good advice Frank.

There is not much that is unpredictable about an R-134a conversion. The outcome is very predictable; marginal a/c performance is assured!!!

DJ,

TF007's recommendation is right on. The folks at Arizona Mobile Air (ACKITS.COM) are pros, knowledgeable, and sell great stuff at the most reasonable prices I've Googled or BizRated.

On this and other forums there is a lot of good guidance on DIY AC maintenance and repair. Please avail yourself of this great body of knowledge. The point I guess I am trying to make is this: If you are going to go through all the hassle of O-ring changeout, it might be a good time to R/R the major compontents and do preventive maintenance.

You don't give any indication of your level of AC DIY, and I'm still learning every day, but here are some of my homework notes and thoughts you might mull over:
+ Cars pre-1994 such as my older MB's were designed to run R-12.
+ Most older US model MB's have GM-style R-4 rotary compressors. These apparently come in two manifold types, flat and stepped. Clearly the seals needed at this location must match the type.
+ Some folks say nix on the R-4, that those from Hodyon (Hancock Industries) are better.
+ I got my R/D and XValve from either Fastlane or ***************, both good suppliers.
+ Study for and take the 609 certification test online. That gets you the legal ticket to buy R-12.
+ Best advice I've read: when tuning up the AC:
- ID the four zones in a mobile AC system and inspect each, by component, for road damage, wear (chafing), and leaks.
- Professionally recover the refrigerant. You can do it DIY but the gear is about $1,000 per refrigerant type.
- Break open all the fitting lines and inspect O-rings. I use one of those small, segmented plastic boxes (like an egg crate), label and insert for later measurement and reference when buying replacements.
- Remove, inspect, note numbers, dimensions, and maybe photograph the compressor, receiver/drier, and expansion valve. Do not discard until the new replacement items come in (about $250). Stuff should match.
- Do a zone and component system flush generally along the lines of that shown in Diesel Giant's pictorial. He uses aerosol canned flush; I prefer liquid in a $40 flush gun operated by shop air.
- Note his recommended lube. This magic potion goes into the compressor, the receiver/drier, and the O-rings get dipped in it prior to component fitting assembly.
- Reassemble with a friend, especially mounting the new compressor -- unless you're a masochist. Torque fittings to, but not over, spec.
- Evacuate to 29"Hg for an hour. You can rent a 4hp vac from Autozone or buy one online, about $250-$350.
- If you have it, do the nitrogen thing to get all the H2O out.
- Charge by weight -- the best -- or by gauge -- less reliable in older systems. Do not overcharge.

And, after all this is over, if, on a 90 degree ambient high humidity day, you don't get 36 degrees at the vent :cool5: ...or less, start doing push-ups... ;)

Good luck.

Awesome advice Frank. I really appreciate the time you took to guide me through properly refurbishing my A/C system. I would certainly have left a few things out or would have tried to short cut others without reading your post.
I have had some A/C experience professionally but I haven't done any major work in nearly 20 years. The last job was a transplant of a complete system from an A/C equipped car to a non-A/C equipped car. I left the evacuation and recharge to a friend who owned a shop. AFAIK the system is still operating on the same charge in that car to this day.