Higher rpm when AC is on - Mercedes-Benz Forum
 
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post #1 of 5 (permalink) Old 06-14-2019, 07:31 AM Thread Starter
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Higher rpm when AC is on

Hello. I have noticed rpm increase on idle when AC is turned on, btw. It is so hot outside, outside temp is >29 celsius. Rpm increase is from 750 to 1000 rpm. Is it normal??
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post #2 of 5 (permalink) Old 06-14-2019, 10:37 AM
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AC on means that the AC compressor is now engaged and loading or stressing the engine a bit more as it is now working and compressing...(extra work required..)

If a normal idle shows 750 RPM without this AC load, adding this extra load would or could stall or stop engine if it did not accommodate this extra load..


A touch more HP (with increased RPM..) to accommodate the added load of the AC compressor....seems logical to me...
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post #3 of 5 (permalink) Old 06-15-2019, 11:32 PM
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mine increases 750 to around 800. but I heard clogged ac compressor or anything makes the serpentine belt difficult to turn could cause higher rpms. It is rarely above 25 celcius here so I don't know if it'll rise to 900-1000 rpm above 30 celcius.
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post #4 of 5 (permalink) Old 06-16-2019, 05:31 AM Thread Starter
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When it is 25 celsius, rpm look like yours, max 800 rpm.
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post #5 of 5 (permalink) Old 06-17-2019, 05:51 AM
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Yeah, I'm thinking that's way too much RPM rise. A 50 RPM rise would be more reasonable and expected. This shouldn't change that much depending on temperature. The AC compressor either runs or doesn't. The load, AFAIK doesn't change with different temperatures.

The clogged AC compressor theory sounds reasonable. Too much pressure/gas in the system, clog in lines or an AC compressor issue?

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