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S430 103K; E320 Wagon 143K
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Discussion Starter #1
2000 S430, 70,000 miles: We bought this car 3+ yrs ago with 52,000 miles, so we only drive about 6,000 miles yearly. We love the car, but were disappointed with its subpar A/C performance. Had to put on Lo setting + Max fan speed on the hottest days. I had A/C serviced & was told everything is working normally, only needed a small amount of refrigerant & that MB just don't have really cold AC. Posts on Benzworld & riding in other Mercedes seemed to confirm this, so we usually just drive my Black BMW on hot days because of its much colder AC.

We had a coolant flush at purchase and again a year ago done locally. On the latest flush, they used the green Prestone. My Indy told me they should have used Mercedes coolant or Zerex, so I decided to re-do it myself.

After draining & flushing the system, I carefully refilled with the engine running and system set at 90*, then went on a short test drive. I noticed the car was blowing cool air despite the 90* setting and temp needle at a normal 82*C. This couldn't be good, so I headed home. On the way, my console displayed "Low Coolant", "Check Coolant" then the system began blowing hot air. I reset to our normal 66* driver/68* passenger and abundant ice cold air quickly made everything comfortable despite the 92* outside temp.

When I checked the coolant level, it was normal and for the past month, our AC has worked better than any time we owned the car. It is on a par with other cars (BMW, Chrysler, GM) we had.

I'm not sure how changing the coolant could affect the A/C but if you aren't satisfied with your Mercedes AC, try a coolant change. Don
 

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W221 & Audio Moderator
2013 S550
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10,978 Posts
It is possible that the change of coolant and flush removed some junk from the duovalve, and has allowed it to position itself properly. If it was only partially in the proper position, it could affect your cooling (and your heating in winter).

Just a guess, but that would be mine.
 

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Registered
S430 103K; E320 Wagon 143K
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626 Posts
Discussion Starter #3
That does make sense Skylaw. The heat was always nice & toasty but the air put us on the edge of uncomfortable every time the outside temps went above 90*. Interesting though, that the previous 2 flushes by a dealer and a local radiator shop didn't change anything.
 
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