Changing a/c drier & switches 1990 300SE; need advice
 

I have a 1990 300SE which has an a/c leak. It stopped working yesterday and I noticed the dye around the receiver drier/accumulator. The previous owner had the system charged in '07 or '08 and they put the dye in at that time. I took the car to a shop today where they told me the a/c high/low pressure switch was bad. The cost to replace the switch and recharge the system is $340 plus tax. Instead of just replacing that switch I want to replace the temp sensor/aux fan switch and the receiver drier/accumulator also. I want to do that myself then have them charge the system. I will also replace all related o-rings and seals. I'd like to know if it's OK for me to do this job myself. I just hate having anyone replace anything anymore unless it's absolutely necessary. I've had too much bad luck with these guys not doing the job they were paid to do.

If you're asking if it's legal, have the shop recover the refrigerant and then take it home. Replace the parts that need replacing, then take it back to them for evacuation and charging. This would be totally legal.

That said, if you do this you need to understand that the filter drier must be installed and sealed last thing and evacuate ASAP! This is because as soon as it is unsealed it beguns soaking moisture. The faster you evacuate after drier replacement, the less moisture will be soaked into the drier.

Hope this helps.

Thanks for your response.
So, since the system has leaked enough where the compressor won't turn on because of a lack of refrigerant, is it not possible it's empty? I certainly don't want to ruin anything, especially new parts. I do a lot of homework before tackling any DIY jobs. The changing of the parts looks to be pretty straightforward. However, your statement about the drier absorbing moisture is the sort of information I'm looking for in order not to ruin anything.

If it were me, I would get a new drier since you have to fill the system.

Yes, I'm changing the old drier and both switches for new OEM ones. I want to know if it's OK for me to do it myself. Any tips and/or tricks would be appreciated.
Thanks for your response.

I don't know if it's a gray area, since your system is essentially empty, because it's really not "empty" just because there is no pressure. You're supposed to pull a vacuum during extraction. Not a complete vacuum like you need to do for evacuation, but a pretty good vacuum at 10 or 20" (depending on the licensing need of the technician doing the job). Even an "empty" system will have refrigerant in it, just not under pressure. But I'm sure that people take things apart all the time when they have leaked out, without sucking them down with the extractor.

Yes, you can do it yourself, but you'll need some tools. As Larry said, it is important to keep the plugs in the dryer until the last minute, when you're ready to put it in and immediately evacuate the system. And don't hold it under vacuum for a period of time to test the system for leaks or for any other reason. A vacuum means that air can be drawn in, with its moisture. After achieving the desired vacuum level (or waiting an appropriate time if you lack a micron gauge), immediately let the refrigerant in to break the vacuum.

Yes, if the system is low enough for the low pressure switch to interrupt the clutch circuit it is VIRTUALLY empty, but there is still refrigerant present.

As I recall the Federal Law requires 10" Hg for one minute, or something like that, for it to be considered recovered. In the old days before EPA intervention, we would have simply released what was left, do the repair, evacuate and charge. What would have been released would have been only a few ounces. People do that today, but they are violating Federal Law. If anyone recommends that you violate Federal Law it won't be me.

The fine is something like $10,000 if caught, and the reward to the snitch is several thousand.

Good luck,

If I recall correctly, 10" is the required vacuum to achieve during extraction for non-licensed equipment used for a non-licensed application. If a license is required for the work (for example, you're getting paid), you must use certified equipment, and that equipment will draw 20".

Also, I recall that the fine is more like 25K per day. 10K goes to the snitch. That's quite an incentive to turn in your shop if you see them doing improper work, but I don't think it's really aimed at consumers.

I thank you and LarryBible for your responses. It seems like I'm going to have to trust someone to do this. I obviously want it done right. So, after reading your responses I've come up with another question. Should I have them pressure test the system for leaks before they do any work? The shop that I took the car to didn't do a pressure test. The guy just saw where the die was and said I needed the a/c high/low switch; the pressure test at the receiver drier with 2 spade connectors. Of course I need to change that, but I also want to put in a new drier and aux fan switch at the receiver drier.

Pressure testing is best done with dry nitrogen and a few ounces of R22. The R22 is so a sniffer can find any leaks. But presence of dye is a very reliable sign of a leak, so you might be fine just replacing what you know to be bad, plus the dryer of course. It's not very uncommon for a pressure switch to leak.

You probably noticed that I didn't really answer your question. I think that it's an optional step in your situation. It will cost more up front, but if another leak is found during the test, it will save you money in the end.

The truth is, if there's another small leak somewhere and the current charge lasts for a year or so, I wouldn't mind. I want to change many more a/c components, but don't plan on doing it now as I have enough other work to do on the car.
Thanks once again.

Honestly, if you are opening the system due to switch/oring leakage... you need replace as all the o-rings underhood at minimum ALONG with the receiver/dryer and said switches. Dryer must be replaced when the system is opened.

Now, if this is really your only problem (which it probably is not), you should be fine to recharge and motor on. W126s almost always leak at the expansion valve as most shops are too lazy to remove it to reseal it, then reinstall. This will REALLY test your patience in this heat, but the effort is well worth the reward.

Plus, how much oil is actually left in there due to the leakage? And WHAT oil is in there as you cannot mix oils? What refrigerant is in there after all these years?

It is probably not what you wanted to hear, but just doing it halfassed means you will be doing it again soon enough. I am doing my SD in this heat, only a few hours a day... but a flush, reseal, vac, and charge is really not that much work. I am being proactive by replacing my R4 before it dies as it is starting to make some funky sounds...

Lastly, please do not use any of the junk replacement refrigerants. Use R12 (do not worry, it is cheap all things considered), the M103 powered W126s are pretty much unacceptable in terms of vent temps in the summer with 134A or anything else. If you are totally anti R12, use 134A so at least you can service someplace in a pinch if you had to do so.

Thank you for your reply.
I believe I've been ambiguous in my responses. In one instance I stated that I wanted to do it right. In another I mentioned that if the repair and recharge lasts a year or so until I can do a more complete job I would be happy. I certainly don't know how much is involved, but the more I can do myself the happier I would be. If the first thing I must do is have someone evacuate the system then I will do that if it will allow me to do the rest of the work myself. I would be happy to change any o-rings, seals, valves...under the hood that I can get to. I don't want to remove the dash at this point. I do have that planned for later and have already begun purchasing parts to do it. I know, there are a LOT of them.
Oh, and I have NO intention of using anything other than the R12 that the system was meant to run with. There have been numerous shops that I have called who have asked me to do the conversion. I will not do it.
I really haven't looked at this a/c system much further than the drier and two switches near/on it. I don't even know where the expansion valve is. I have read more than one post stating that if the expansion valve isn't leaking one shouldn't bother it.
Any help and recommendations are greatly appreciated.

Since it is hot and you want a temp solution, I would just swap the easy stuff up top, vac it down, and charge up until the winter rolls around. Once winter is around, properly go through the system.

Luckily the M103 has an excellent style compressor attached, the only downside of it in the W126 is there is a huge area of the condenser that is not covered by the fan shroud due to the small radiator and mechanical fan. I have been on the look out for a replacement fan with the three bolt style to simply pull more CFM, BMWs are close from the same time frame but the blades are facing the opposite direction. :rolleyes:

The expansion valve itself rarely goes bad, it is simply the orings that run to it that fail and begin to leak... and shops say 'oh your evap core leaks, $1500 please' 20 year old orings simply do not seal well. I would not rebuild the system without swapping the orings, they are not too terribly difficult with the proper tools and PATIENCE. Frustration leads to cross-threading. Every one of my 126s has come apart with black orings still scattered about... even my dealer maintained 300sel that had an 'evap core leak' ;)

You must simply hand start the upper two connections on the TXV that run to the evap core first, then hand start the low side line. I have found THAT is the only way to easily do it, no other way works. There is more than enough slack to wrangle in the small liquid line once the other three are snug.

The dash does not come out, simply that knee bolster thing and the side carpet that covers the center console. Just grab yourself a few 20-25" box fans to keep yourself cool. :)

Excellent on the R12, accept no substitute in these cars unless you totally go through the system to convert... $$$$$, even then I do not think it is smart. Anyone with a high school education should understand the cost involved between retaining R12 and a full 134A system is simply not worth the expense.

Thank you.
So, after reading responses to this thread and about a dozen others, I have found that the best thing for me to do right now is to repair what is clearly damaged/leaking. That means sticking to my original plan of changing the drier and two nearby switches. Anything that comes apart will be replaced correctly and that means new o-rings and seals where applicable.
Now, I understand my system could still be leaking at the expansion valve and/or evaporator. And, as I stated before, I don't want to get into them now if I don't have to. What I'd like to know is if they are leaking, would the leaks normally be slow? That is, approximately how long would this new charge last if one or both of those components are leaking? Is that something that the a/c mechanic will be able to tell me after testing the system?