'81 300SD Why replace drier? - PeachParts Mercedes-Benz Forum

tyl604 · #1 03-05-2017, 10:49 AM

My 1981 300SD - freon leaked out last summer or so and I have not replaced it yet. Then last week I found the pulley (maybe clutch) had gone and that was what was causing all the bad bearing noise. I have cut the belt for now and the noise is gone.

I will replace the compressor this summer.

So is it always necessary to replace the drier and why? I seem to remember that on my old Cutlass I just opened up the top and replaced something - maybe a desiccant package?

Would this drier have water in the bottom or what exactly prevents it from being reused. Is it always 100% necessary to replace it in a case like mine? (It is cheap - maybe $25 - but would be easier just to leave it in.)

Bigdaddybenz · #2 03-05-2017, 10:58 AM

MOISTURE!!!!....... If the freon leaked out there is bound to be moisture in the system..... Replacing the drier kinda goes without saying..... Once you evacuate the system, and install the new freon, with a new drier your air will be frosty cold..... Also, since your system is empty now, it would be a great idea to replace all of the o-rings (it aint that hard) and replace the expansion valve (which is a ***** to get to as I remember replacing mine) it is located under the driver's side dash...... Sounds like lots of extra work but it's so worth it.... I cannot tell you how many times that I half-ass did my AC on those older Benzs..... but once I did it properly, the results were amazing, my 300SD blew cold air that would rival a new car's AC system!!!!!..... good luck

jake12tech · #3 03-05-2017, 11:03 AM

The receiver drier is the filter of the AC system. It traps moisture, any foreign particle or any dirt that's in the AC system. It goes without saying, anytime any major AC component is replaced, you replace the drier. It's cheap.

Dan Stokes · #4 03-05-2017, 11:15 AM

What makes it a dryer (often a receiver-dryer but not sure on the Mercedes system) is a desiccant package built into it. If you'll note, in most of those in the past 35 years or more it's a sealed can and is not serviceable. At some point the desiccant gets used up and can hold no more water so you would start circulating water thru the system. Is yours at the point? No way to tell so the thing to do is just change it out. As stated, not big money.

Dan

tjts1 · #5 03-05-2017, 01:02 PM

If you can put the system system under under a deep vacuum and hold there for an extended period of time, it'll dry out the dryer. Shops replace the dryer because time is money.

tyl604 · #6 03-05-2017, 01:41 PM

Thanks guys. I think Dan more caught the flavor of my question which was more technical. So the drier does in fact hold a desiccant which may be loose or may be in an individual container inside the drier. The way MB designed it the drier cannot be opened up and the desiccant package replaced. That was actually my question.

I will probably replace it and then open up the original to peek inside.

So far I have not found a place in Atlanta that will pressurize the ac system yet; very odd. No one seems to be interested. I have some freon so it will be interesting to see if some shop will put it in for me. I got rid of my freon can attachment and hose a long time ago and folks like Pep Boys do not even carry them.

97 SL320 · #7 03-05-2017, 02:43 PM

Your Olds was pre 75 ish and had what was called VIR ( Valve In Receiver ) , this was the expansion valve in an aluminum block and the dryer below. In the day GM loved units to have lots of parts in one package as it speeds up assembly line output. ( wiper motor with washer pump - wipe delay circuit built in , distributor with ignition coil- electronic module built in , alternator with built in regulator. )

Over time, moisture will make it's way through rubber hoses, this is the primary reason the dryer should be changed. Opening the system isn't a primary reason to change the dryer, it is just convenient to do so at that time, just be sure to replace the oil that was lost.

I would not expect the dryer to give off much moisture under vacuum. At atmospheric pressure, silica jell ( do not eat ) desiccant must be baked at 180*F ish to dry it out so I would not expect this temp to drop to room temp under vacuum. AC units might not even use silica jell because at typical temps, it would be regenerating leaving moisture to circulate through the system. Moisture in the system will lead to the formation of acids and corrosion from the inside out.

ROLLGUY · #8 03-06-2017, 12:10 PM

Most A/C DIYers fail to realize that the entire system needs to be flushed whenever a major component (compressor) is replaced. Especially with an R4, and definitely when changing from R12 to 134a. All the oil needs to be flushed out, as well as any contaminants from the failed compressor. It is also a good idea to pressure check the system before and after replacing components. It is a great possibility that one or all of the hoses leak, and should be replaced as well. Be aware that 134a molecules are smaller than those of R12. While they may not leak with R12 in the system, they may/will leak with 134a.

ROLLGUY · #9 03-06-2017, 12:19 PM

Another thing, an R4 does not have its own oil sump, so the oil is circulating in the system, lubricating the compressor. When the refrigerant leaks out, so does the oil. You have no idea how much oil is in there, so that is another reason for flushing. Too much or too little oil in the system can cause problems. Also, the oil needs to be matched with the refrigerant used.

tyl604 · #10 03-06-2017, 01:11 PM

Roller - I will go with freon; we all know that the SD system does not cool as well with R134a. I have 48 oz which I remember as reading someplace that is what the system takes.

As far as I know the compressor is fine except that the pulley/clutch is gone. Not sure how that could cause contaminants in the system since it did not blow apart.

The freon escapes as a gas. It is not intuitive to me how the mineral oil or pag (do not remember which) which is not a gas could escape unless it leaks as an oil from a connection. When I installed a new compressor about 15-20 years ago I took it to my Indy who vac'd it out and recharged it with freon. So I do not know if he added oil or not.

Right now I am struggling to find a place which will pressurize the system and look for leaks. They all want to vac it out which I know is not appropriate for finding leaks. Then again I am not going to do anything until it gets hot in Atlanta so I am not in a great hurry.

ROLLGUY · #11 03-06-2017, 02:22 PM

Quote:

Originally Posted by tyl604

Roller - I will go with freon; we all know that the SD system does not cool as well with R134a. I have 48 oz which I remember as reading someplace that is what the system takes.

As far as I know the compressor is fine except that the pulley/clutch is gone. Not sure how that could cause contaminants in the system since it did not blow apart.

The freon escapes as a gas. It is not intuitive to me how the mineral oil or pag (do not remember which) which is not a gas could escape unless it leaks as an oil from a connection. When I installed a new compressor about 15-20 years ago I took it to my Indy who vac'd it out and recharged it with freon. So I do not know if he added oil or not.

Right now I am struggling to find a place which will pressurize the system and look for leaks. They all want to vac it out which I know is not appropriate for finding leaks. Then again I am not going to do anything until it gets hot in Atlanta so I am not in a great hurry.

When a clutch bearing fails, it puts undue pressure and vibration on the compressor shaft and seal. I would suspect that the compressor will fail shortly after a replacement clutch, if that is what is done. Replacing the entire compressor with a new one is a good idea, replacing it with a Sanden would be better in my opinion. Again, no one knows how much if any oil is in there- not you, me, or the previous guy that worked on it. You can continue to throw parts and refrigerant at it every season, or you can start from scratch and do it right the first time, your choice. I am just here to share my knowledge and experience. It is free, and you can take it or leave it. I won't fault you or anyone either way......Rich

tyl604 · #12 03-06-2017, 02:57 PM

Pep Boys has an R4 compressor for about $150. I think it was Pelican that had a MB for about $400. So I will replace the compressor. Someone told me that you used to be able to buy a clutch and just replace it but no longer can do. Not interested in that but unless you could do that without removing the compressor, it would not make much sense as you would lose all the freon when you remove the compressor to install the new clutch.

So I agree with you; compressor is the way to go.

Junkman · #13 03-06-2017, 04:00 PM

Rich,
What components are not included in your conversion pkg? I have 2 SDs. One compressor is locked. The other (son's) hasn't come on in years. I expect that it is likely shot also.

I drive one daily and promised my wife that it would have good AC this year. The other may be for my 15 yr old and he also would like to be cool. I have some time to get my son's ready but time flies. No way he should be even close to driving.

tyl604 · #14 03-06-2017, 05:28 PM

Rich - isn't it also necessary to install some kind of special support system to hold the Sanden compressor - which makes it a lot more difficult than just switching out the R4?

ROLLGUY · #15 03-06-2017, 07:27 PM

Quote:

Originally Posted by tyl604

Rich - isn't it also necessary to install some kind of special support system to hold the Sanden compressor - which makes it a lot more difficult than just switching out the R4?

Junkman too-
I sell the bracket kit, compressor, hoses, and other parts to make a complete system.