Mercedes-Benz has a chart that 'suggests' normal vent temps based on ambient temperatures.

Your 45°-47°F vent temps are pretty good. I have an adjustable switch on my A/C that allows me to bring the auxillary fan in at a lower temp/pressure. This and a GOOD fan clutch help tremendously.

Keep in mind that a W116 will overheat without a fan, even at 60-70 mph, so the fan is critical at road speeds too, though many will argue the point.

Regards,

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

Thanks Bert.... I have a 603 engine , 300SDL, W126
As the car was overheating at higher speeds I changed the radiator, pump and T-stat (Behr 80 degrees)...
and through magic cooling temps are down to normal (about 90 C at all speeds!...even when I am driving 90 mph for some time).

This somehow affected my AC vent temps as a side effect.
Vent temps dropped by about 2 degrees C or 4 F. I can tell because here are the same conditions all the time...there are 2 days with partially rain..but the rest of year it is sunny and identical, boring and hot as hell.

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CENSORED due to not family friendly words

A recent shot of my W116 center vent on a 90°F day with 21% humidity...

Attached Thumbnails

 

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

Hi Dr. ,

I was testing if I could improve my fan clutch on my 300 SEL 3.5. If this experiment is successful I'll also do the clutch on my 300SDL. I agree that this clutch needs to work properly. No question. At speeds and hot the fan must 'haul' and stop at the moment when the engine stops. Anything else causes problems.