1979 - W123 - Need starting advice/instructions on rehabing my AC - PeachParts Mercedes-Benz Forum

DieselPop · #1 07-14-2010, 02:18 AM

Hello,

My AC is one of the last things I'm getting to rehabilitating in my used car...

I'm very much a beginner with AC problems and diagnosis, so some advice on where to start would be most appreciated. I'm looking for the "most bang for the buck" starting strategy to asses the condition of everything and then where to go from there.

Basically, I don't detect any cold air coming from the vents. As I've never been in a working 300D's cabin when it's on, I don't even know which vents the cold air would be coming from. Would it be the center vents? My heat/defrost works great in the winter, and only blows from the outside vents on either side.

So... where should I start, or what should I ask to have tested or done at a competent shop? Should I just start by having it recharged with coolant to see how long this lasts, or should I have a shop test the system to give me an estimate of what I need? I have seen a sticker under my hood indicating that the system has been changed to R134a, I think it's called? What does this mean? Is it more eco-friendly I hope?

Perhaps I should ask for a flush, evacuation, then recharge at a shop? What should this cost me if I have it done?

I have a bad feeling the compressor is probably going to be shot... how much are these to replace?

In other words... do people owing these cars end up spending more than a thousand usually to get it back into working order?

Any advice on where to start narrowing down what I need would be of great help.

Thanks.

weird beard · #2 07-14-2010, 03:30 AM

I am not familliar with MB a/c systems, but I am VERY good with a/c in general.

You need to find out if it has any refrigerant left. If it does, your a/c is sound and you have a mechanical or electrical problem that needs to be sorted out. Given the age of the car, chances are it is empty.

First, you need to find out where the a/c went. You would just be wasting your time having it recharged. If no leaks are found, make sure the system is dyed with UV tracer dye. If it leaks out, it can be pinpointed with a uv light.

Second, if the unit has a drier, have it replaced. Make sure this it done only after the leak has been found. Being open to the atmosphere will have saturated it. The only time I wouldn't replace it is if it causes more damage replacing by breaking off lines etc. If it comes out well, replace it.

Do not use the off the shelf fix you a/c in a can crap. Leak stop is only for selling the car. Fix it properly. Don't let anyone talk you into using that junk. Also, don't use the "replacement" a/c in a can refrigerant. It is just refrigerant grade propane. Some states ban the use of it in automobiles do to the potential fire hazzard if you are in a crash. It is otherwise safe to use. You can smoke away without fear. A/c leaks are usually so small, you would not even be able to set the leak on fire. The propane is also molecularly smaller than the microscopic pores in the rubber hoses. It will leak out.

Depending on the availability of R12 (the old bad for the ozone stuff) in your area, you may consider converting to R134A (the new not so bad for the ozone but bad for the mechanic stuff). I have done this. All that is required is to remove the R12 oil from the lines ar add a converting oil, and recharge with 60% of the rated R12 capacity. You don't need to change seals, compressor, lines, etc. It will work just fine.

How much this is going to cost depends on what parts (if any) are needed. A/C lines can be made and it is generaly cheaper than buying premade ones. Get them out in one piece and take them to a hydraulic hose specialist. Most do A/C lines as well. They can make them up while you wait.

Make sure the person you are having do the work knows what they are doing. If they try to use the crap in a can, walk away. No, drive away.

Aquaticedge · #3 07-14-2010, 03:30 AM

well, the first thing is to Determine if your Compressor is shot before delving into the rest, giving that it's been converted to 134a means that someone took out the original refrigerant and replaced it, which from what I have read will likely caused your compressor to Grenade, I am not too sure on how to check the Compressor, I dont know if you are able to turn it by hand if it's charged or not, someone will chime in on that matter, but look into putting R12 back in the system or the compressor will likely break sooner then it should.

weird beard · #4 07-14-2010, 03:39 AM

The compressor will turn by hand when fully charged. Just make sure you are trying to turn the clutch and not the pulley. To check if it opperates, jump a power and ground to it.

Now to start an off topic discussion, I have never had a problem converting units to R134A. The key is to drain the oil from the compressor. The R12 oil will "chunk up" when exposed to R134A. Drain it out of the compressor and lines. The compressor has its own internal oil supply and it must be drained and replaced.

#5 07-14-2010, 07:13 AM

Yes, MOST old auto systems can be converted to 134a and sometimes this is even successful. In the case of the car in the original post, it is one of the worst possible candidates for conversion.

The 79 and earlier 240D's had York/Tecumseh compressors. They are very good and cheap to replace, but the problem is that they do NOT hold up well to the added high side pressure that comes with a conversion to R134a.

Any a/c diagnosis begins begins with connection of manifold gauges to get system pressures. The pressures along with the ambient temp at the time of reading will tell quite alot about the condition of the system. If static pressure is low, the clutch will not engage to start with, so some REFRIGERANT, not coolant must be added.

If you can find an auto a/c shop in your area, they can do an initial evaluation for a very small fee.

Keep us posted.

DieselPop · #6 07-14-2010, 09:10 PM

Great -- thanks for all the advice guys. It sounds like I should check the operation of the compressor, and also see if I can check the pressures or lack of any pressure in the high/low sides.

How much would a "manifold gauges" set cost for home use? Do they market them for home mechanics? I'm wondering also if some major chains (Autozone?) might have lenders one can borrow?

I just did a search in the online yellow-pages, but it occurs to me I can't seem to find a search team that would bring up shops that specialize in AC cooling systems? Any ideas on terms that would narrow down my hunt?

I live in Portland, OR. If anybody reading this just happens to be from Portland and could recommend a good shop, that would be greatly appreciated also.

Thanks Again.

leathermang · #7 07-14-2010, 10:33 PM

Quote:

Originally Posted by weird beard

The compressor will turn by hand when fully charged. Just make sure you are trying to turn the clutch and not the pulley. To check if it opperates, jump a power and ground to it.

Now to start an off topic discussion, I have never had a problem converting units to R134A. The key is to drain the oil from the compressor. The R12 oil will "chunk up" when exposed to R134A. Drain it out of the compressor and lines. The compressor has its own internal oil supply and it must be drained and replaced.

It is nice that you want to help..'
but you need to do some research on the MB system in question first..

it has NO OIL SUMP... and you can not just drain the lines.. to get it out you must use a solvent flush and power it out with preferably with something dry like nitrogen.....

DieselPop · #8 07-15-2010, 06:19 PM

Shoot, is there nobody else that can offer me advice on my further questions with this!?

Thanks.

zeke · #9 07-15-2010, 07:30 PM

for your purposes, harbor freight will have a manifold set for very little $$. McParts places will only have 134a sets, but you need the R12 hoses -- unless you convert to 134a, then you will need to refit your valves with the quick connect style and get the appropriate hoses.

search function could be your best friend if you try it.....

Yak · #10 07-15-2010, 08:22 PM

Quote:

Originally Posted by zeke

for your purposes, harbor freight will have a manifold set for very little $$. McParts places will only have 134a sets, but you need the R12 hoses -- unless you convert to 134a, then you will need to refit your valves with the quick connect style and get the appropriate hoses.

search function could be your best friend if you try it.....

Actually, he probably needs 134 gauges. Something about a sticker saying "converted to 134a."

So...read this page: http://www.aircondition.com/tech/questions/82/

Decide whether this is something you want to troubleshoot yourself, or pay someone to do for you. If you're going to jump in, then get some gauges, take some pics of your compressor, take some readings and report back. Harbor Freight advertises a 134 manifold set for $50.

You may run into a situation where your car was "converted" but they only swapped out the low-side valve to a 134 valve, so the gauges may not hook up. I have that and a few others report having the same thing. If so, you'll need to get an extra high side port to add a place to hook the 134 gauge. It's another few bucks at any chain parts store - maybe $10-15.

If, like Larry says, your car uses an older-style York compressor and yours is bad, you can find them here for $360 http://www.allpartsexpress.com/ShopByVehicle.epc?q=1979-MERCEDES--BENZ-300d--/--L5_3.0l_diesel-Climate--Control&yearid=1979&makeid=MERCEDES+BENZ%40%40MERCEDES+BENZ%40%40X&engineid=1193699%40%40300D++%2F+L5%5F3%2E0L%5FDIESEL%40%40300D&catid=Climate+Control&subcatid=A/C Compressor&mode=PA

(That's a link to All Parts, a site sponsor, IAW the policy on linking parts to the sponsors).

That site also shows an R4 compressor, so maybe yours has the R4. There are cheaper sources for other compressors, but Phil gives good service, so give him a shot at supplying your parts.

You can get adequate cooling with 134 from a W123, but the experts will say the best cooling comes from R12.

Cooling effectiveness of the refrigerant is one factor, the effect on the life of your compressor of higher pressures required by 134a is another factor. You'll get opinions on restoring back to R12, or just staying with a 134a conversion. It's your car, in your neighborhood, with your money; so ask some questions and choose what works for you.

If your system is dead and you want to restore it. The Diesel Giant pictorial on flushing your system is a good reference. It uses Freeze-12 as a refrigerant, which will generate some controversy, but covers the basics of a thorough flush. It waaaaaay understates the mess associated with flushing, but it's nothing a competent DIYer can't handle.

Since you express a concern about eco-friendliness, don't vent your system, regardless of 134a or R12 (it's illegal, and messy when pressurized oil vapor sprays out) capture your oil - you may want to measure the quantity anyway. A shop can recover/vacuum test your system before you crack any lines open. You'll pay a little, but you're doing the right thing.

Note: spraying pressurized 134a-driven oil vapor refers to my experience with an accident damaged condenser, not illegal venting. My "what is this cr*p all over everything..." experience with removing oily front-end parts gave me an appreciation for what a little oil and pressure can do.

Wear goggles.

#11 07-15-2010, 08:56 PM

I have hesitated to say much in this thread for several reasons, but maybe I can offer some help.

The particular situation you are in is not insurmountable, but it's sure not a best case for a first a/c repair attempt.

To start with, determine what compressor your engine has. On the early 123 cars, they used a sort of cube shaped York type compressor mounted on the upper passenger side. Beginning somewhere in the 1980 model year they went to an R4 which is a hockey puck shaped compressor mounted low on the drivers side.

The York compressor models I've seen were 240D's with manual temperature control. I've never seen an ACC early car so I can't tell you what compressor they had.

Once you identify the compressor, you still need to evaluate the condition and you need gauges for this step. You have an odd situation with only the low side 134 adapter. If you decide to use a permanent adapter fitting on the high side, get a brass one. They are available at the good auto supply stores that cater to the shops, not ones like Auto Zone.

The alternative would be an adapter fitting that you can use on your gauges and not leave permanently on the port. What you would need would be a fitting that is typically used on a vacuum pump to adapt to 134 acme thread manifold gauge fittings.

Be warned that the second alternative above is technically illegal because Federal Law requires the fittings to correspond to the refrigerant there in.

Again, if you have a York type compressor it will be short lived with 134. I've seen several of them fail under these conditions, while I've seen ZILLIONS of them outlast the car they were installed on when they were used with R12.

IF it is the York compressor, it does indeed have a sump. It has an oil fill plug and there are many places where you can find dimensions for making a dipstick.

Hopefully I don't get flamed here, but you seem to need some help so I'm trying to offer it.

Identify your compressor and post back here with that information. We can then go from there.

DieselPop · #12 07-15-2010, 09:47 PM

OK. Thanks for responding to my plee for more advice!

I just took a look under the hood and I think I may be in luck in that I got the later type compressor? There is nothing but my alternator on the passenger side, and just below the power-steering pump there is a unit which seems to be the compressor. One of the pipes going into it runs across the front and top of the engine, just to the rear of the radiator..?

I also looked more closely at the sticker near the dreaded "climate control unit". The strange thing is that the sticker is printed at top "converted to Freeze 12", but in one of the fill-in boxes below this, it says the recharge compount was 134... I wonder what this means?

My climate control unit looks to actually be in pretty decent shape with no obvious cracks... so I'll have to cross my fingers there on that. That unit has to also be working, even if the compressor is working and it will hold a recharge without leaks right?

It sounds like I should find a competent shop to do a clean out of the system and then a vacuum test for leaks as a first diagnosis leading to other steps? Where does having the later-type compressor (what are they called?) put me?

#13 07-16-2010, 07:10 AM

Okay, we're making some headway in identifying more about what you're working with.

My early 240D's, both had manual climate control and York compressors. Yours has the automatic climate control like the 300D's of the day had. Since I've never laid my eyes on the early 123 ACC system I'm not sure if they have an R4 or what, but it sounds like it.

The other important information you apparantly found is that the Freeze 12 junk was put in, but very wisely taken out.

What part of the world do you live in? The reason for the question is to determine what type climate you have to deal with.

showme · #14 07-16-2010, 11:14 AM

I'm presently in the same boat, and have been digging through the forum, and have found a couple of helpful things. First thing I'll say is that Larry knows his stuff, so listen to him.
Secondly, I ran across a post the other day, and the two things that were mentioned was the control panel, (mine's an auto), and how they are known to need cleaned or resoldered sometimes, and that they are fixable and there are a few help articles in the "Resources" section at the top of the page. I also read that there is a control switch (?) of some kind that can be the culprit of not letting a good compressor switch on when it's supposed to. I'll try to find that article and post it's link. Then there's my buddy, the owner of a body shop, who also does my AC work, who informed me that he has come across a few cars that previous owners, (or maybe their unscrupulous AC repairmen) have only changed the low pressure fitting over to R134 without changing the high pressure fitting, and in reality had not correctly drained (flushed) the system, but had just added the 134 to the R12, which does NOT mix, and probably ruined any new compressor what with all the junk that was not removed and the non-mixing oil. Anyway, I bought a new control panel that I'm getting ready to install. Then I found the DIY control panel repair article and other good threads on how to do it. Listen to Larry's advice. But it could also be a control switch, the "foam tube" that utilizes the cabin sensor, or the switch controlling the condenser, which I am now looking for. Not to mention the AC\heat control valve, (which is an easy fix if your ac is blowing HOT air continuously). Hope this doesn't confuse you. The one thing I'll say is that the guys on this forum are the best. I'd have sold the 300D a long time ago if it weren't for this place.

showme · #15 07-16-2010, 11:28 AM

Okay, since I'm too computer illiterate to figure out how to send the link, the thread I told you about is by Treeman on 7/11 and is titled "82 300td question Help". I was on it just yesterday (7/15). Look under Resources (top of page) under DIY Articles, then down to the '123 Chassis' section, then AC climate control repair. Good article. Sounds like you've got a compressor like mine.