W108 AC conversion - Mercedes-Benz Forum

 
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post #1 of 7 (permalink) Old 06-27-2011, 02:28 PM Thread Starter
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Date registered: Feb 2010
Vehicle: 1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
Location: Williamsburg, VA
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W108 AC conversion

I am resigned to the fact that I must retrofit my AC to R-134. My compressor has a bad seal and apparently the PO did a half way conversion meaning nobody wants to touch my car with R-12.

I can not find a source for the original receiver/drier for this car. Everyone says it is no longer made (inlet in top, outlet in bottom, 3/8"flare fittings, 2" OD x 9" long) so I am planning to adapt a drier from a mid 70's vintage 450SEL (is shorter and squatter, but has more volume).

My research has led me to the conclusion that I must do the following: Replace compressor, replace the drier, flush the evap and condenser, inspect expansion valve, replace hoses (mine appear original and I don't trust 40year old barrier hoses), add a high pressure cutout switch in lieu of the superheat switch (which has no purpose with R-134), and recharge with approximatley 90% of original charge using PAG oil (150 viscosity). Also thinking of replacing the 12" aux fan with a larger electric one.

Am I missing anything? Anyone have results of a properly done conversion? I know you will lose some cooling capacity, but it has to be better than what I have which is none.

None of this is hard or expensive, but I really only want to do it once.
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post #2 of 7 (permalink) Old 07-05-2011, 04:41 PM
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Vehicle: 1973 220D
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I updated my '73 220D (York compressor) all I need to change was to rebuild my evaporator and replace one hose. I had already replaced some of the other hoses in previous years.

My mechanic had no problem retting it rebuilt.

I don't know that you really need to replace the fan. Why not do the conversion and see if it runs hot? The fan is unrelated to the rest of the AC.

Mine now works fine but here in CA it might not be as hot as TX.


Frank Flynn. Poet, Artist & Mystic
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post #3 of 7 (permalink) Old 07-06-2011, 08:08 AM Thread Starter
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Date registered: Feb 2010
Vehicle: 1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
Location: Williamsburg, VA
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Did you go back with R-134a or stick with the R-12? I was considering replacing the aux fan because the condenser seems to be the limiting component in the R-134a conversion so I want to keep as much air going across it as I can when in stop and go traffic. Not too woried about overheating so much.

I am adding a high/low pressure switch in the system and think I know how I will incorporate it into the circuit. I'll let you know how it works.
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post #4 of 7 (permalink) Old 08-31-2011, 09:26 AM Thread Starter
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Vehicle: 1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
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Well, the conversion is complete. Put in a new Four Seasons rebuilt compressor. Could not find a drier that fit in the stock location so modified the condenser to accept a 1976 450SEL drier. Had new hoses built by Nostalgic Air Parts. Added a new aux fan switch to the drier as well as a hi/lo cutout pressure switch in series with the compressor clutch. Flushed the evaporator and condenser. Blew air through everything for a few minutes and then drew a vacuum for about 2 hours to ensure all the flush was truely gone. Added PAG 150 oil and R-134a. She blows VERY cold and all appears good. Still need a new blower switch as mine has given up the ghost and I have the blower jumpered to run a full speed right now, but it all works as it was intended to.
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post #5 of 7 (permalink) Old 08-31-2011, 10:22 AM
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well done. I discovered my system has been converted by previous owner and just had mine recharged with R134a. blows nice, strains the motor a little when it is running, as in, you can feel it in the pedal that the motor has a bit more of a groan to it, increases engine temp but its managable
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post #6 of 7 (permalink) Old 08-31-2011, 12:12 PM
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I did go with R-134a and it is working well. I live near San Francisco and it doesn't get totally hot here so the first real test I got was last week when I took my son to college in Oregon. Several places along highway 5 were over 100 and the AC worked well but I suspect I need a new / rebuild blower motor.

The air temp (I happened to have a temp probe) was 40 degrees. But the wind coming out just wasn't that strong, the first and second settings are almost the same, the highest setting was stronger but nothing to blow you away.

This is a '73 220D and the blower is a dual squirrel cage with the motor in the middle located under the center console. I can spin the cage by hand and I do notice it is stiff (will not spin very freely) but there appears to be no way to lubricate it without taking the motor out which appears to be somewhat difficult.

Any opinions?
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post #7 of 7 (permalink) Old 08-31-2011, 07:20 PM Thread Starter
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Date registered: Feb 2010
Vehicle: 1972 280SEL daily driver. 904 Dark Blue with cognac interior. euro 4.5 engine
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The blower for the W108 is in the right hand pasenger foot well. It is separate from the heater blower. Mine blows quite a lot of air.....fortunately.
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