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

Greg in Oz · #1 10-11-2004, 04:50 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, 05:30 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, 11:22 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, 05:47 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, 06:01 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, 11:10 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