R12 System - Evacuate or not?
 

On my W126 300SEL The air is not cold.

The compressor kicks on but I am not getting much cooling if any, I know theses systems are somewhat complex but it seems to me like the appropriate vents are opening and closing based upon the different modes.

I have 2 cans of R12 but have read that "topping it off" is not advisable because you are not filling to the proper level and I don't have enough coolant to replace all of it. I also cannot seem to find a shop that will mess with R12 to even evacuate it properly.

I live in NC and want to daily drive this car but the summer here is no joke.

I spoke to a shop that suggested I just top off the R12 by adding it to the low side and watch the sight glass carefully to ensure the bubbles dissipate and call it good.

I am floating in the dark here as my expertise here is very limited.

Chris

If you evacuate, are you going to capture what’s in there? Or vent it to the environment? I don’t think it’s easy to find a place that will capture it anymore. I could be wrong.

The reasons for evaporating are to assure you have the right mass and also assure the system is dry. My opinion is that if the system is still pressurized on the low side, then you are unlikely to have taken on significant moisture. I think evaporating this time of year is a horrible idea, since the hotter it is, the easier it is to evaporate any water in the system. Only evaporate if you have no pressure. That’s my VERY unprofessional opinion. Charge it by the low and high side pressures, and do everything you can to minimize r12 in our environment.


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Are all of your vacuum pods actuating correctly? Check the recycle door. Verify the monovalve is closing too when on Max AC. Fan clutch actually work? Few do with age... a hint? Sachs ones are the only that work in my experience, spend the extra money for them. Also use the later fan for the M103.

Clean the condenser, the dual fan ones are a prick to do. Just do it. The evap needs a cleaning at this point too. 'Evap Powr-C' works boss for this procedure, just pick up a hand actuated container and wand to apply. It will take work, but worth the trouble.

If you have a leaky system, save the R12 for now. You probably have original orings and a leaking compressor. BTDT. Reseal the entire thing while it is cool out and flush it. Seriously. Use a syn compressor oil. Mastercool for the vac pump and Yellow Jacket or MC for the gauges.

A quick, cheap charge is with 152A if you just need to get by...did this in the 300E for years before it met its demise. Multiply your charge weight, 2.9lbs on the W126 by 0.54 and that is your 152A charge. Yes, it is air duster. It works as well as R12 pressure wise and cooling wise. You need two full, 10oz cans and one half of another. The last you have to meter in via pressure. I use R12 charts. Now if you can find 12oz cans, you are perfect. Two of them is pretty much full. Three, 10oz cans at my local Walmart are $12.

BTW, the car will never cool with faulty recycle and defrost pods. Tint will help cool the W126 vastly also. Even a mild 50% quality film.

Before getting all carried away, grab hold of the return line up by the brake booster and see if it's cold and/or sweaty. If it is, you know you have a problem with the air doors, OR you have an issue with the monovalve not shutting off all the way. If it leaks through, the amount of heat the heater core throws is enough to cancel out any cooling that takes place from the A/C system.

Are you also CERTAIN that the compressor is coming on? You see the center section of the pulley pull in and start spinning? If you're low on refrigerant, it's likely that the compressor will cycle a lot.

I would rather capture it but I have not researched how.

So I assume there is a procedure to check the monovalve and the vaccum pods in the FSM?

Will do on the condenser.

Plan to tint to 35%

The center section is definitely spinning. Don't know if its pulled in or not. Ill have to look again tonight.

Thanks for all the pointers everyone.

The pulley ALWAYS spin on the compressor. Just because it's spinning doesn't mean the compressor is engaged. Look at the center hub of the pulley. With the compressor off it will be stationary. If the compressor is engaging, you'll see it suck in and start spinning with the rest of the pulley.

Great points.

I just assume the worst with 30 year old HVAC systems. :)

For sure! But if the system still has a charge of R12, I sure wouldn't be emptying it unless I had to!

https://youtu.be/f5VsbD5RVu8

The compressor is spinning. ^ I have not noticed it cycle off at all unless the a/c is turned off.

The high pressure line is not cool or sweaty

The low pressure side is cool not the high side. The low side line is the larger. The high side should be hot.

My mistake. I was feeling the correct line I just assumed that the larger line carried the higher pressure. Here is the diagram from the FSM. I assume the expansion valve is in the dash somewhere?

https://farm5.staticflickr.com/4608/...55894a2a_b.jpgUntitled by ttownthomas, on Flickr

here is what is happening at the sight glass

https://youtu.be/0rq8Zh4llh4

And I checked for the presence of 12v at the monovalve. It has 12v at max cool and 0 at any setting other than max cool.

That just means that the controller is sending the correct signal right? The controller is telling the monovalve to close but it may not be functioning correctly? Is there nay way to test the monovalve itself?

I will say that the heat did not seem to work correctly either during the cold spell we had 2 weeks ago.

Low side with port is under the hood by the second firewall, driver side. Close to the brake master cylinder. High humidity it should sweat...like a cold Miller Lite on a hot summer day. :)

High line is post condenser, much smaller OD and runs in and out of the dryer. It should be pretty hot to the touch with a working system.

This is my opinion from personal experience and logic. Ditch the R-12. You will probably not find anyone that is licensed or willing to evacuate it. Sorta like trying to purchase a new 8 track tape or VCR. R-12 is done. Sooner or later the compressor will go, if it already hasn't, then what? You need not switch to R-134a either as it is junk in our old systems. What I have done after struggling with extreme heat in southern California desert is get rid of the converted R-134a in my system and run R-152a (Air Duster). I have posted on the site of the great success with the temps cooling way more than the 134. R-152 is plentiful, cheap (just got two 10 oz cans for less than $8.00), and you can release it freely into the atmosphere without fear of ozone depletion. Also, you can continue to use whatever oil is in your system to carry it. I am using PAG oil. I actually just bought 2 cans a few days ago because I noticed a small leak of oil at the suction line connector, I think I crushed an o-ring. But this o-ring swap will not be a $200 o-ring swap like it would be if I was running r-134. Use logic and think of the pros and cons of running the R-12 vs R-152. Good luck. PM me if you have questions for me personally about my conversion.

I have no aversion to switching to a non-tradidional refrigerant. Once I figure out if my system is functioning correctly I will definitely reach out.

The way to do that at this point is to get a set of gauges and find out what your pressures are. Since you know the compressor is actually running there's gas in the system. OR there's an electrical fault. The original problem with my SDL was a stuck KLIMA relay that let the compressor run with no refrigerant. It turned the compressor into a hunk of melted and galled aluminum.

If you convert to a new refrigerant, you've got some work in front of you. At the very minimum, a flush of the system to purge the mineral oil out and a new filter dryer. If you want to do it right, all new O-ring seals and a new expansion valve rated for R134a should be added to your list.

I've joined the list of people who don't understand the aversion to R134a. If the system is converted properly, it works fine, at least in the Gen II 126 with the small-tube condenser. My SDL cools better than my Honda does. Even on a 110˚ day, it has no problem keeping up and I have no window tint. I've run R152a and R290 (propane) and found them both to be lacking at lower speeds in the city.

My plan for this weekend is to get a set of gauges, check the pressures and manually check the function of all the pods from the FSM.

Did my sight glass video confirm that there is something in the system? I have no frame of reference.

The sight glass video suggests that there's not much refrigerant in the system.

Actually I would just hook up the freon and fill it while watching the bubbles disappear in the sight glass. At most you might lose a can of freon.

That thing is basically empty, sub 1lb easily. BTDT on my SD.

It will take more than two, 12oz cans of R12 to fill it for good cooling...you need 46oz for a total fill (four, 12oz cans).

When was the last time it was fully charged? Are you sure R12 is actually in there?

Yes, 46 oz sounds right for a full charge. However I suspect with a can or two you can tell if it is actually going to cool.

If it does not have new connectors (like for R134A), could it have something other than freon? I have no idea. If the OP has maintenance records, that might help answer.

So I guess I agree with the NC shop who in Post #1 recommended he just try topping it up with freon. What can it hurt? You have to start someplace.

I bought it from a dinky dealer on a bring-a-trailer auction. From the carfax and the documentation that came with it, it looks as thought the PO was an elderly gentleman who owned it from new and it was only serviced it only at a MB dealership until 2 or 3 years ago. Then a couple of months ago his daughter donated the car in the san francisco area where it sold at an auction. Perhaps he passed? I dont have alot of detail, just 1-line records of bi-annual services at the dealerships. I can tell the car was very well loved but best guess it sat for 2-3 years with little use in the end. I feel strongly from my digging around that no shade tree techs have worked on this thing. It has R12 fittings.

I think that's the answer.

R12 fittings do not equal R12 in the system.

Hopefully the records will detail some work.

This. My car runs 134a and still has the stock fittings. I HATE the conversion fittings, so I left it with the R12 fittings. If I ever sell the car (unlikely) I'll put conversion fittings on it.

Check the radiator bracket to see if there's a sticker somewhere saying it was converted. If a shop did it, there should be a sticker saying what kind of gas they put in it.

https://farm5.staticflickr.com/4628/...d42e67bb_b.jpgUntitled by ttownthomas, on Flickr

Pulled the monovalve today. The seal was torn. I assume this is part of the problem and that this is allowing coolant to bleed into the heater core during "max cool" and other various cooling operations.

Gauges arrive tomorrow.

I don’t know why so many people act like r12 is gold and not obtainable. It’s easily purchased on eBay. Buy a few cans and recharge your car. If it leaks out again, find the leak, fix it, and recharge your car by weight.

I’ve done the r134 conversion and it’s ok at speed, but is useless in traffic. I don’t have much experience with drop in substitutes but generally more of a hassle than it’s worth.

You need a license to buy R12, even from ebay.

My 1991 300se has envirosafe es12 in it, installed by the previous owner, and it seems to work well. Not as good as r12 but better than r134. I had r152 from canned air in my 1979 300d, it worked well too except when sitting in traffic for long periods of time.

Got my AC recharged and working today in the 92 300TE. It was already converted to 134a, so I just loaded it up. Was trying to figure the proper charge, by weight of 134. Just happened to check my parts car, a 93 300E with a factory 134a system.... folks, the entire systems are IDENTICAL, except the compressor oil and refrigerant. Same evaporator, same condenser and fans, same compressor. 92 calls for 2.4lbs of R12, 93 calls for 2.2lbs of 134a.

I’ve never been asked once for my license when I purchased r12 for my 89 300e on eBay. At least 2 different occasions. Further, the “license” is a $15 fee and a ridiculously easy open book test.

True or false: it’s ok to vent more than 10 lbs of refrigerant in to the atmosphere

If you can answer that, you are golden.

I agree, but I still took the test and got my 609 cert.

Remember big brother's always watching :D

Here are the pressures with the motor off
https://farm5.staticflickr.com/4670/...552fbe15_b.jpgUntitled by ttownthomas, on Flickr

And with the car running but the HVAC system off - center of pulley NOT spinning
https://farm5.staticflickr.com/4666/...b49b24a3_b.jpgUntitled by ttownthomas, on Flickr

And with HVAC set to max cool - center of pulley spinning
https://farm5.staticflickr.com/4676/...f2517133_b.jpgUntitled by ttownthomas, on Flickr

What was the temperature outside? You are definitely low. The low side should be like +30, and high in the 200 psi ish range

Definitely very low. For it to be that low, you probably have a leak somewhere too. I'm surprised the compressor is engaging with the pressure that low, the pressure switch on the receiver/dryer is supposed to keep the compressor from engaging when the system is very low.

Around 60f

Am I thinking right here:

Since the compressor dosen't run when the a/c is off I think that means that the electromagnetic clutch on the compresser is good.

If the car was drained completely of freon and the compressor still engages we know that the pressure switch must be bad.

I might as well fill it with 152a and dye see if it cools and find my leaks. Drain it again and Replace the A/C seals and the pressure switch.

If I do this how do I know if the proper amount of oil is remaining in the system? It it as simple as removing the fill hole screw and filling it up?

The clutch is good because it engages the compressor. The controls that engage the clutch are questionable, I'd expect at the pressures you have that the clutch would be disabled. I bring it up because if you run it for long like that, you risk tearing up the compressor. It relies on gas circulation to return oil to the compressor sump. When I got my SDL, the Klima relay was stuck closed, so it ran the compressor with no refrigerant and burnt it up. That happened long before I got the car. The compressor was a write-off and the system was a mess. Don't let yours get to that point, it's a lot of extra work that doesn't need to happen.

If you want to do a quick gas & go, buy a couple cans of R12 and top off the charge. See how long it lasts before it leaks out again.

If you're going to have the system recovered and filled with new gas, you might as well do the job right. Flush the system out, replace ALL of the O-rings (they're a common leak point), replace the expansion valve with a new one (all the new ones are R134a rated), install a new receiver-dryer, and replace the fan switch and pressure switch on said receiver-dryer (the newer switches have pressures matched for R134a). Pull a deep vacuum, dump in some PAG oil and refill with R134a. The small-tube condenser on the Gen II 126 works fine with 134a, and when matched with the correct expansion valve, the system works very well.

I agree with all your points but gassing it up the way it is will not solve the problem with the compressor running all the time right?

Here is my plan:

I want to keep running r12 but I need to fix my leaks and replace all the seals first. but before any of that I want to see if the system is functioning correctly.

I want to pull a vacuum on the system and then fill it with 152a and dye to find all my leaks AND test the rest of the system.

What do I do about oil with the 152? Should I check the level at the compressor when it is empty? Just add a little for good measure? What oil should I use?

If you change refrigerants, you need to flush the system and refill with PAG oil. 134a and 152a both require PAG oil. R12 uses mineral oil. The importance comes with how the oil circulates, R12 is miscible in mineral oil, so it is carried along with the gas charge. 134a and 152a are not miscible in mineral oil, so it will not carry it through the system. You run the risk of starving the compressor for oil, or oillogging the condenser or evaporator.

If you're sticking with R12, stick with R12. I did that originally in my SDL, but after about a month and a half of use, the expansion valve got stuck open and stopped cooling. You can't buy a new R12 rated expansion valve (different orifice size than R134a), so I converted the system at that point. When the conversion is done correctly (flushed, filled by weight, correct expansion valve) there's not much difference in performance on these later W126's. Early 126's and the W123's had a crappy condenser that was barely adequate for R12. The Gen II's have a small-tube double-circuit condenser that's much more efficient with the newer refrigerant. The SDL cools just as good if not better than most modern vehicles in my climate and I don't even have the windows tinted...

By "flush the system" you mean take it apart and flush all the parts manually? No reason not to replace stuff at that point. Are their quality aftermarket parts or will I need genuine MB parts (reciever/dryer & expansion valve) for this?

Flushing the system involves opening up the lines and sending a flush solution through it. It isn't difficult. You'll want to drain the sump of the compressor too.

After flushing, replace the O-rings, pressure switches, and receiver/dryer. There are decent aftermarket parts out there. Modern replacement parts are designed for the pressures and lubricants used in 134a systems, just another reason to convert it if you're going that far.

FWIW I ran the 300E on mineral oil and 152A until it met its demise New Years Eve. That was three years worth on the original compressor.

You would be fine to charge it and get it cooling.

If I charge it with 152 and then evacuate again will I contaminate somthing?

Well, if you evac it into a machine with 134A, yes. You will destroy their recovered refrigerant...but seeing as how 152A comes in air duster cans, you can just release it into the atmosphere and it is no big deal. :)

Initially I had 134A in that 300E as it was all I had on the shelf. It leaked out, so that is when I tried the 152A. Cheaper and worked better. R12 would be better, but for $15-30 for a 12oz can versus $2-5 in...it was a no brainer for me. The car cooled very nice for me.

Make sure the condenser and radiator are clean. Need to pluck the rad to pull the condenser far enough back to pull the dual aux fans. It is worth the hassle. Also, the only fan clutch that worked for me on the M103 was the Sachs. With no air flow over the condenser, you will have weak AC always.

To educate myself and to be able to buy R12 I went ahead and got 609 certified. It was easy. I read the booket (about 60 pages) and took the test.

I have decided that putting R152a is not worth the risk. Perhaps the EPA is being over zealous but they feel that it is a safety hazard to run it in a system that runs the R152a through the passenger cabin. Apparently it is flammable under certain conditions.

I figure Ill just run it the way it was designed. From what I have read I think the compressor on these things is supposed to run all the time unless:

1. The AC is switched off
2. The high pressure side is below about 40psi (mine was at 50)
3. The receiver dryer gets over a certain temperature

Plus my pulley does not "retract". It either spins or does not spin so they must have changed compressor designs at some point in the life cycle of the W126.

Anyhow. I charged up my system with my 2 cans of R12 freon and injected some dye in the system. Presto - Cold air.

Now Ill watch for the dye and how fast it leaks out and then Ill repair the leak and evacuate and recharge with a fresh R12 charge by weight.

Nice, glad you have conditioned air again. :)

I believe you are on the right track. If I remember right, they used to have freon with "stop leak" in it. Whether it worked and did not harm the system, I know not. Just a thought. Good luck.

Yours is easier than mine on my '81 300SD. I had a terrible squeak which I thought was the water pump. Turned out to be the compressor. So I cut the belt and now need to replace it. Not to hard; just tedious.