Resurrecting a dead A/C - Where to start? - PeachParts Mercedes-Benz Forum

Diseasel300 · #1 03-26-2017, 12:02 PM

Ye olde Diseasel went on its first road trip in 10+ years yesterday and it became apparent shortly into the journey that the A/C needs fixed. The question is where to start, what should I be looking for, any special considerations that need done "while I'm in there"?

Car in question is an '86 300SDL (W126). Right off the bat I'm already replacing receiver/dryer, pressure switches, and Schraeder cores. Additionally the compressor is completely locked up. Can't budge it even with a cheater bar, so I'm assuming I'm in for some cleaning and/or flushing. The question is what should I be doing to get all the old crap out of the system?

I'm just going to get a new compressor, not worth trying to repair or rebuild the one that's in there. I have a 30# can of R12, so I'll be going back with R12 refrigerant as well.

The condenser, evaporator, expansion valve, and hoses/joints are all dry (no oil) so they appear to be in good condition, however I'll change out the O-rings as a precaution.

So the question is: How to flush/clean this system? Surprisingly in my 20+ years of working on cars, I've never had a compressor failure or had to deal with anything like this. I can fix leaks and swap out a clutch or failed components, but I've never had to clean up after a compressor failure!

Maxbumpo · #2 03-26-2017, 03:23 PM

Go to FLAPS and get a flushing product, disconnect as many components as possible, flush each with the product and follow up with compressed air or dry nitrogen to make sure you blow out all the stuff. You can chase it with alcohol and more air / N2 to make sure you've got all the crap out.

Get the right oil, I think it is 40 weight for OM60x engines.

Oil up each o-ring as you install, pull a vacuum, add oil to replenish each component per the chart in the factory service manual, add some N2 or test refrigerant to make sure the system is leak free.

There are leak detector / sniffers that are pretty cheap, like $30, might be worth getting one of those to make sure you've got it leak free under pressure.

funola · #3 03-27-2017, 12:01 PM

If you are willing to do a little fabrication work first, this method http://www.peachparts.com/shopforum/diesel-discussion/380881-vacuum-flush-ac-system.html made flushing the AC system neat and easy.

Diseasel300 · #4 03-28-2017, 12:04 AM

I had actually thought of doing something similar to this, but since I'm going to have every joint apart to replace O-Rings and what-not, I feel like it's a better use of my time to just flush everything out individually, especially since I have no idea what the system is like until I break it open. I do know that the compressor is seized solid. Not sure if it got moisture in there and seized over the last decade it sat, or if it seized up in use. I do know that when I got the car the plug to the compressor was disconnected. I think that's a pretty big clue!

The other big deterrent is the expansion valve. Don't want to wreck that since I'm not converting to 134a. All the aftermarket or replacement valves I've looked at are set up for 134a. IMO 134a sucks as a refrigerant for an A/C system. Get up to 90-95˚ outside (which it does for 50% of the year here) and it simply cannot cool the car anymore. I've converted a few systems over to it over the year, and all of them were unsatisfactory IMHO. The people who drove the cars were satisfied because it was better than nothing, but I'm the type that likes to hang meat in my car when its hot outside.

leathermang · #5 03-28-2017, 09:22 AM

The AC thread in my signature used to be pinned to the top of the forum.... years were spent accumulating the info in it...

Diseasel300 · #6 03-28-2017, 11:50 AM

A lot of very good information in that thread. Reaffirms some of what I already know and learned a bit more. Hopefully enough to be proficient instead of dangerous

Parts are now on order.

Compressor, O-Rings, Receiver/Dryer, A/C flush, Pressure switch, Fan switch, Schraeder cores, Castrol mineral oil, red Nylog, and new hoses for the manifold gauge set.

Should be set up to make a stab at getting it working in a couple weeks when everything makes it here and I have a chance to work on it.

BillGrissom · #7 03-28-2017, 09:23 PM

Unless your hoses look pristine, I would change any original 1986 rubber hoses. I did so on my two W123 cars, exc. the small "liquid line" which looked OK. You can buy "barrier" hose stock on ebay and use Oeticker stepless ear clamps if you don't have access to a Master-Cool ferrule crimper. The factory crimps can be cut off w/ a cutoff wheel or hacksaw and prying, then reuse the metal fittings. HBNR O-rings (grn or blu) are best, even w/ R-12 mineral oil. PAO 68 oil would let you use any refrigerant in the future.

Diseasel300 · #8 03-28-2017, 10:54 PM

The hoses are in excellent condition. No dry rot, no oil sweat, no rubber checking or cracking. I debated redoing the rubber lines and decided against it, mainly due to the fact that I'm sticking with R-12. If I were converting to 134a, it would be a no-brainer. The bigger concern is the O-Rings, which I'd imagine are 31 years old and hard as rocks. Every O-ring I can get my hands on (without pulling the dash) is being replaced.

ah-kay · #9 03-29-2017, 02:18 AM

Quote:

Originally Posted by Diseasel300

Every O-ring I can get my hands on (without pulling the dash) is being replaced.

I am not trying to be cynical but what is the different with NOT replacing any at all? Oil ring seldom fails. What makes you think the one hidden under the dash will be good? I would leave them alone. They don't move nor rotate, unlike o-ring on the compressor shaft. Even compressor shaft o-ring lasts many many years.

Diseasel300 · #10 03-29-2017, 10:26 AM

No cynicism taken. My experience with O-rings hasn't been as good as yours. Every time I've dealt with a leak, it's always been a weeping O-ring or a leaking Schraeder core. Except on the SL, which has a leaking compressor seal.

Since I'm gonna be in there cleaning anyway, I may as well just do all the O-rings I can get to. My thoughts do largely agree with yours regarding anything lurking behind the dash though. Since they're usually inside the car and not out in the engine bay and weather, they're less likely to have an issue. I've never dealt with a leak inside the car, they've always been under the hood (usually at an O-ring!)

funola · #11 03-30-2017, 09:44 AM

Quote:

Originally Posted by ah-kay

I am not trying to be cynical but what is the different with NOT replacing any at all? Oil ring seldom fails. What makes you think the one hidden under the dash will be good? I would leave them alone. They don't move nor rotate, unlike o-ring on the compressor shaft. Even compressor shaft o-ring lasts many many years.

I am surprised to hear this from you. You can well expect 30 year old o-rings on AC systems to be deformed, dried out and not sealing well. If you have a system that requires a re-charge every year or 2, chances are the o-rings are the culprit, not the hoses.

I have pressure tested about 10 used W123 AC hoses under water (with new o-rings). Some of them looked really bad on the outside, not one of them leaked.

Diseasel300 · #12 03-30-2017, 10:23 AM

Quote:

Originally Posted by funola

You can well expect 30 year old o-rings on AC systems to be deformed, dried out and not sealing well. If you have a system that requires a re-charge every year or 2, chances are the o-rings are the culprit, not the hoses.

I have pressure tested about 10 used W123 AC hoses under water (with new o-rings). Some of them looked really bad on the outside, not one of them leaked.

This is why I'm going the route that I am. Even the '83 SL has gas-tight factory hoses, but had leaking O-rings (and ultimately a failed compressor seal).

The gas and oil going back in the system is what the hoses were designed for. I'm not worried. If it were 134a, I'd be a bit more worried about leaks, but still probably wouldn't bother unless the leaking was excessive. I'm not worried about a top up every year or two.

funola · #13 03-30-2017, 12:05 PM

........ I'm not worried about a top up every year or two.[/QUOTE]

With R12, that can get expensive.

Diseasel300 · #14 03-30-2017, 12:07 PM

Not when I have a full 30 pound can that's been sitting in the garage since the late 80s. This car is the only one that uses R12. SL's compressor is dead and see no point in fixing it since it's a "fair weather" car. That R12 can sit in the can, or it can get used on something useful. Doesn't cost me a dime either way.

ah-kay · #15 03-30-2017, 12:13 PM

Quote:

Originally Posted by funola

I am surprised to hear this from you. You can well expect 30 year old o-rings on AC systems to be deformed, dried out and not sealing well. If you have a system that requires a re-charge every year or 2, chances are the o-rings are the culprit, not the hoses.

.

That is why I wrote to replace ALL the o-rings if you and the OP believe they would be dry or crack. Every o-ring is subjected to the same harsh conditions, hidden or not. personally I only replace the one which I open up. It is just me. May be it is only me, but it never failed me.

2 years top up may be a bit too short but one would expect Freon to leak. It is the porous nature of the hoses.