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Rebuilding system on 1989 Merc

JonathanL on Sat June 28, 2008 5:54 AM User is offlineView users profile

Year: 1989
Make: Mercedes
Model: 500 SEC
Engine Size: 4976
Refrigerant Type: R12
Country of Origin: United Kingdom

Hi,

Wondering if anyone can run me through rebuilding my A/C system as I know very little about it.

The system is R12 which from which the refridgerant leaked out years ago. I will have to run it off R134a though as you cannot get R12 here any more.

I have a new compressor and condensor (both were leaking) and will be replacing most, probably all, of the pipes.

Actual bolting together of the system seems pretty striaght forward but I have a few questions;

a) the box the compressor came in says to drain the oil and replace with the manufacturers reccomended oil. What is this? Is it the oil which is distributed throughout the system with the refridgerant or a different oil that lubes the compressor bearings or something? What oil do I use?

b) am I correct in saying that the filling valves on an R-12 system are different from those used on R134a? If so do I use some sort of adapter on them or do they have to be changed? If they need to be changed how is this done as the one on the new condenser seems to be permenently attached?

c) When ordering new pipes should I order direct from Merc, who will presumably supply original pipes intended for an R12 system or should I go to a specialist and have new pipes for R132a made up?

Any other advice appreciated.

Cheers.

J.

Karl Hofmann on Sat June 28, 2008 4:08 PM User is offlineView users profile

Hi John..

What compressor do you have there? I would say that it would be better in the UK to stick with PAG oil so if you let us know which compressor you have then we can advise which oil.

Regarding the service ports, you can get screw on R134a service ports that fit over the existing ones but I find that they are a pain in the bum, In the UK there is no requirement to change the service port as long as you label the vehicle with which refrigerant is used.

You could check with merc to see if they do a later pipe for your vehicle, but expect some pretty steep prices, was your model vehicle made after 92? when R134a was used? but I would be inclined to stick with your existing hoses if they are in good shape, depending on where you are a good aircon man could rebuild your existing hoses with barrier hose..

Karl

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Never knock on deaths door... Ring the doorbell and run away, death really hates that!

Edited: Sat June 28, 2008 at 4:18 PM by Karl Hofmann

Karl Hofmann on Sat June 28, 2008 4:25 PM User is offlineView users profile

The compressor should be a Denso 10p17 so I would use PAG46 in that one... Just checked

-------------------------
Never knock on deaths door... Ring the doorbell and run away, death really hates that!

rwhyde on Sun June 29, 2008 4:21 PM User is offlineView users profile

Jonathon,

I see you have a new condenser,...
I'd suggest you consider getting a condenser from either a later model MB or a parallel flow condenser and adapt it to your vehicle. I have an '89 300SE that I converted about 3 years ago but am finding it is only suitable up to about 90 degrees and then it just isn't sufficient. I'm in Texas and during the summer out high temps surpass that everyday, so we don't drive the vehicle much. The original condenser is the tube and fin design and was only marginally adequate with R12 on the warm days-in my opinion. It only really got cold when operated for some time at highway speeds-even when new.

I've been researching alternatives and taking measurements. It appears that a condenser from a 96-98 210 e-Class is of a later design that worked well with R134a and should fit in the space reasonably well. One slight complicating factor in changing condensers is that the original MB condenser provided for the high pressure connection port to measure pressures in the condenser. If you use a universal condenser then you would need to accommodate for that.

Depending on your weather conditions you may find 134a suitable-but us folks in the southwestern US need serious A/C.

Karl Hofmann on Sun June 29, 2008 7:54 PM User is offlineView users profile

The tube and fin condenser will be fine for the UK weather.. If we get to 30c then our roads melt

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Never knock on deaths door... Ring the doorbell and run away, death really hates that!

JonathanL on Mon June 30, 2008 5:00 AM User is offlineView users profile

Cheers for the advice chaps.

Karl is quite right. Realistically, cooling up to 90 deg is quite acceptable here as it rarely gets hotter than that for more than a few days a year.

The A/C in my car will probably get used more for demisting the windows and keeping the interior de-humidified than actually cooling thye occupants!

J.

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