Air Conditioner- RPM drop

[DWJoy]

When I turn on the air the RPM drops to 400 and sometimes the engine dies. What could be my problem? Is their aomething that should boost the idle when the air is on?

 

[HBarlow]

You didn't provide any info on the year and model you own so it will be difficult for anyone to help.

I've owned an '01, '06, and '08. The ECM adjusts engine idle speed to compensate for AC loading keeping the idle speed constant. I don't know if earlier mechanical injection engines did the same.

 

[fest3er]

(Assuming the problem A/C is on a Cummins... . )

With as much torque as the Cummins produces, the little bit the A/C uses is hardly noticed. If my engine ever dropped even 150 RPM or so when the compressor kicked on, I would be very concerned and would very quickly suspect the compressor's bearings.

And as near as I can tell, there is no A/C compensation on 12V engines.

 

[DWJoy]

Sorry I did not provide more info. My Ram is a 1996 Cumins with automatic trans with 180000 miles.

 

[GOlsen]

Idle speed may be too low. In drive with the a/c on, rpms should be 750 or so. What RPMs are you seeing before you turn the a/c on? And no, there is no automatic compensation for the a/c, you just turn up the idle speed.

 

[DWJoy]

The idle speed before air turned on is about 650 and drops to about 400 when air is turned on. I will try to turn up the idle and see if it helps. This just started and the idle speed has always been about 650. It dose idle a little rougher than before the ULSD. could that be part of the problem with the lower cetan of ULSD?