When the A/C refrig pressure is displayed on the CC (item 7), on my E320, it reads in range 14-16 bar when car is at IDLE at say a stop light.

Then, when I pull off, the pressure drops to the 6-7 bar range.

Considering the engine and possibly the compressor are now running faster, why does the pressure drop? Just trying to understand what is happening.

Secondary question - On a new car, would there be a similar drop in pressure?

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Does your car have a belt driven fan? If so the fan is spinning much faster when moving. Plus you get the airflow over the condenser from the wind. Both of those lower its temp, which lowers the high side pressure.

I'll have to look at that reading in my Passat. It has twin electric fans so their speed isn't dependent on engine speed, and they're very powerful to cool the engine bay during a 1100*F DPF regen.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

My E320 also has twin electric fans in front of the condenser. Air flow would also likely make some difference I guess.

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5

But there's no belt fan behind the radiator? From what I have seen the smaller pusher fans don't pull as much air because the fanwheels can't be very thick.