Air conditioning advice sought - '90 W201 - PeachParts Mercedes-Benz Forum

Greg in Oz · #1 10-11-2004, 03:50 AM

I purchased my 190E during the summer before last (Jan '03) and noticed that the air conditioning was not very cold. I did not worry about it too much until early last summer when I had it re-gassed (and was told pressures and everything looked fine). It worked great for a couple of months but then its performance began to deteriorate again. It is still running with R12. With summer again approaching, I want to get it sorted. Being someone who does all my own repairs and maintenance (apart from work such as auto tranny rebuilds and air conditioning) means I don't have a known and trusted workshop for this work. A fellow club member does still have some R12 and is prepared to re-gas it for me but is concerned with the slow leak. I asked if he could put dye in the system to locate the leak but he feels the leak is so slow it will be difficult to find. He is also of the opinion that it will probably be the compressor seal and that a new compressor may be required. The car has travelled 226,000km (about 140,000 miles) since new in 1990 and I have no reason to believe the compressor is not the original. My 300TE is the same age but has travelled 184,000km presumably also with the original compressor (both cars have similar Nippondenso compressors but that in the 300TE is slightly larger). The 300TE has had R134a retrofit prior to me purchasing it in 1998. It cools perfectly and I have only had refrigerent added once (several years ago) in the time I have owned it.

My questions are:
1. Is it a fair call that the compressor will be at fault?
2. Can a leak that takes several months to prevent the system working, be detected with dye or by any other means?

I don't want to start throwing lots of parts (and lots of money) at it. I would prefer to only repair whatever is necessary. Obviously I could have an R134a retrofit done, but I am concerned with the cost involved, and I also believe this can be even more prone to leaks due to the higher pressures involved and cooling efficiency can be reduced (although the R134a works great in my 124 wagon). The cost of an R12 re-gas every summer rules that out as an option also.

What do the air conditioning experts among the members here recommend (Larry and others)?

AusMBtech · #2 10-11-2004, 04:30 AM

G'day Greg.

To do a R134A retrofit on your vehicle will require a reciver dryer, 2 adapters (for the new style charge fittings), a pressure switch if you don't already have the modified type for Australia, a flush and regas with dye and some oil.

I wouldn't be jumping at a new compressor yet, there are many other seals/orings that can leak(at that are more probable), even the valves in the charge fitting are known to leak.

The dye is pretty good at finding any leak except a leak from the evaporator (W140's do this all the time).

I'm not sure what my dealership charges to do the retrofit (I'm the one who does most of the A/C work) but at least you know that it's done right.

If you want me to chase up the cost of a retrofit then feel free to call me at work (9997 2455 8am-4pm) with your exact VIN so I can get a quote on the parts for you.

Alex.

Jim Anderson · #3 10-11-2004, 10:22 AM

If the system is empty change every O ring you can get to, its a DIY job. There's one on every fitting.

Greg in Oz · #4 10-12-2004, 04:47 AM

Alex,

Thanks for that info. We need helpful guys like you in the club here in Sydney. I hope you do eventually decide to join and that the thought of members hungry for advice and information does not scare you away! Knowledgeable members are highly respected in the club. Many even come to me (as a reasonably capable DIYer) for advice on the models I am familiar with, despite the fact that I am not an automotive tech. If possible I would prefer to stay with R12 for now. Hopefully with dye we can find the leak and that it will only be something simple. If it gets more serious then I may consider an R134a retrofit.

Jim,

The system is not empty. It seems to leak down enough not to cool but not much more than this. Last time I had it re-gassed it still had some pressure remaining in the system.

Thanks,
Greg

AusMBtech · #5 10-12-2004, 05:01 AM

If you can regas with R12 then stick with it because it is a better system, although The benz seem to take R134A better than other cars I've seen.

My 190D has a R134a conversion, I regassed it when I bought it in Feb this year (I just wanted to check that it was full) and it's been fine since. I put my thermometer down the vents on the way home today. It was 4-6degC after extended idling (5mins) and 0-2degC while driving.......The dark tinted windows help alot

I'm waiting to see what happens to the new clutchless A/C systems in a few years. The compressor always runs at 5% to circulate oil in the systems, but when a leak develops the oil can't move through the system and the compressor self destructs

from lack of lubing because there isn't a pressure switch or clutch to stop the compressor when there is low gas. The end result is either compressor, filter and tx valve replacement with a system flush or an entire system replacement.

.........I think I like the idea of the $2 oring leaking and the systems shutting down, don't you?

Greg in Oz · #6 05-02-2005, 10:10 PM

Since starting this thread, I had some more R12 added by a fellow club member and he checked for leaks with a sniffer but found none. He did comment that the low side pressure seemed too low relative to the high side suggesting there could be a blockage in the system, possibly at the TX valve. At the time the cooling performance was poor.

The following day I found the cooling to be quite good although I suspect it could still use more R12 (some bubbles in sight glass). I have been observing the behaviour throughout our summer and for much of the time the cooling performance has been adequate with the compressor and aux fan cycling on and off as expected. I do however find that after an extended period of use that it appears to stop cooling, despite the fact that the compressor continues to run (without cycling off). Sometimes switching the system off for about 10 minutes will allow it to operate again when it is again switched on. I am puzzled by this behaviour and wonder if it could be due to a blockage.

Whilst doing an engine oil change on the weekend and using the opportunity to check everything in the engine bay and underneath, I noticed an oil leak at the receiver-dryer. It is covered with a clean, almost sticky oil which I can only assume is compressor lubricant. I also noticed a slight leak of the same oil at the compressor. I know it is not engine oil as it is very clean whereas the engine oil was much darker being due for a change. The oil on the compressor appears to have leaked from the manifold where the refrigerant lines attach rather than from the shaft and clutch area. Are there O-rings or something here that can leak?

Would it be reasonable to have the system emptied, replace the receiver-dryer and the O-rings at the manifold on the compressor, and then re-gas or should more extensive (and expensive) repairs be undertaken? Pressumably more oil will also be required to replace that which has leaked. How does one know how much oil to add? Any thoughts would be welcomed.

Thanks,
Greg

AusMBtech · #7 05-03-2005, 07:54 AM

Because you need to open the system anyway which requires the replacement of the reciever/dryer I would suggest that you also purchase a set of adapter valves and regas the system with R134a. It only has a minor reduction in cooling performance but will make it easier for future servicing.

There should be 4 orings under the manifold on the compressor. Make sure you replace them with green orings and NOT black orings. The green orings are compatible with both refrigerents while the black ones don't like R134a (over a long period of time).

Don't be worried about higher pressures of R134a, it should only be recharged with 80% of the R12 charge so the pressures remain about the same. The molicule size of R134a is smaller so it will leak slightly faster than R12. (eg 10grams per year rather than 7grams).

The oil should be topped up about 20mls for a slow leak and 40mls for a large/long term leak. The reciever dryer takes about 30mls as well.

Alex.

#8 05-03-2005, 09:02 AM

If you were in the US I would be adament in saying that you should NOT change to R134. The reason is that 134 prices are rapidly increasing while R12 is coming down in price due to the decreasing demand since the cars requiring it are hitting the junk yards in record numbers. I would expect that a similar pricing variance would be occurring down under.

I just bought a 30 pound container of R12 delivered to my door for $425 while 134 is rapidly going up with todays price being around $325. Since the R12 price is only about 30% more, then there is only about a $7 difference for the 2.5 pounds needed for one of these cars. You probably can't even buy the adapter valves for that. Then after you're done you will have a system with at least a 15% loss of cooling capacity. Add to that the fact that statistically converted systems have a much higher failure rate and it just doesn't make sense. A further additional issue is that most MB's do not have much, if any, reserve condensor capacity to make for an effective conversion, depending on your climate.

Yes, the compressor seal is a likely leak, but the seal can be replaced without replacing the compressor.

In my experience for a leak at the rate you describe, UV dye will most likely find it. A red dye with the naked eye will not. Use a yellow/liime UV dye and then search for it with a UV lamp and yellow glasses.

I'm not sure I agree with replacing all the o-rings to try to get lucky and fix the leak. O-rings rarely just go bad on their own. Additionally opening every connection on the system introduces lots of chances to INTRODUCE an additional leak in the system.

Since you now have the system charged, what I would do is add UV dye to the system while it is charged and still working. Then I would immediately run the a/c enough to get a good puddle of condensation water underneath the car in a dark area or at night and then check the puddle with a UV lamp and yellow glasses to see if there is any dye present. If so then you have an evaporator leak or possibly an expansion valve leak.

Another somewhat common source of a leak is at the connection between the bulb and the block of the expansion valve.

Hope all this helps and good luck,

Greg in Oz · #9 05-04-2005, 04:23 AM

Alex,
It's a tough decision. Many recommend staying with R12 and some even go so far as to say they wished they never changed to R134a and would consider changing back. Having said that, our 300TE had an R134a conversion prior to us purchasing it in 1998 and I have always been perfectly satisfied with its cooling performance. Of course, I never knew how it performed with R12. In the wagon it even has a larger volume to cool than a W124 sedan or coupe although it has a slightly larger compressor than that in my W201 (not sure which compressor the 124 sedans and coupes got). The 134a has also only needed one top-up in the time we have owned it. Logic suggests that the appropriate time for an R134a conversion is when the system is open and parts are being replaced. It is just a case of do I do it now when it is being opened for only a receiver-dryer and O-rings or do I wait until when something more major such as the compressor, evaporator or TX-valve requires replacement? Is the amount of oil required also not that critical? I am surprised there is not more "science" involved to the quantities required following a leak.

Larry,
Interesting comments re the price of R12 versus R134a. I am not sure how they compare here other than to say that it seems to be difficult to find someone with R12 and that they charge a lot for it. Our summers in Sydney are fairly demanding on the air-con with humid days reaching up to 35 degrees C (90 F) and dry days sometimes exceeding 40 C (105 F). Based on this and comments by you and others regarding both the loss of efficiency and the greater chance of leaks and other problems with 134a, I am tempted to stay with R12 for as long as possible. It is disappointing that dye was not added with the last lot of R12 but he seemed to only want to add gas and sniff for leaks. The leak at the receiver-dryer is very obvious with the whole unit covered in a film of oil. Whilst the leak at the compressor does not seem as bad, it is enough for some of the oil to have dripped onto the lower engine bay cover and leave a large patch there. Looking closely at the compressor reveals the oil seems to be leaking only from the manifold with the area around the shaft and clutch perfectly clean and dry. This suggests the O-rings at the manifold need attention in addition to a new receiver-dryer. How about I replace just these items (without disturbing anything else) and go with another charge of R12 and oil (hopefully with dye this time) and see how I go? I can only hope that the rest of the system is OK. I don't believe the evaporators in the W201 to have such a bad reputation as those in the W140 or even the W124. Despite the similarities between the 124 and 201, at least in the 201 the evaporator is much easier to access than in the 124. With its placement forward of the firewall it is accessible from below the wiper mechanism (rather than pulling all the dash inside the car). This location also means that condensate flows into the area between the two firewalls and then via the rain-water drains rather than separate drains as in the 124. This would also allow dye to be detected in this area prior to it reaching the ground underneath the car.

Thankyou both for your valued feedback and opinions,

Greg