[DML] Re: RPM Drop When turning on AC
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[DML] Re: RPM Drop When turning on AC



As pointed out, on a properly set up and functioning K-jet system the RPM's may drop momentarily as BOTH the A/C compressor AND the 2 cooling fans kick in together (and the heater fan motor). That's a double whammy on the motor, the A/C compressor and the alternator. What you DO see is scary if you watch the voltmeter dip below 13 volts and the lights dim. If the idle system is operating right you should see the RPM's around 775 but the hunting will change. It seems to hunt a little slower but it seems the RPM's go higher and lower. Never actually measured it. If you do not have idle control I would expect all that load would lower the RPM's more than 50. On many of the older cars (with carbs) they had a solenoid on the throttle arm that would bump up the idle when the A/C was on so the car wouldn't stall.
David Teitelbaum

--- In dmcnews@xxxxxxxxxxxxxxx, "Tom Niemczewski" <dmctom@...> wrote:
>
> On the properly working K-Jet it should not drop at all. The idle control 
> module should keep the RPM constant regardless of load (to a certain point).
> On Megasquirt you should have the A/C compressor connected to the ECU and it 
> should bump the RPM up by about 200 rpm with the compressor running.
> 
> Are you sure the rpm are dropping? It might be just the tach gauge. When the 
> A/C is running, both cooling fans are running with it. That causes a voltage 
> drop and when the connections are not clean and perfect will cause a 
> significant drop in the instrument cluster. With lower voltage the gauge 
> might show strange things.... lower, higher, jumping around. So, make sure 
> the rpm are really dropping before you start tearing things apart.
> 
> Greetings from Poland!
> Tom Niemczewski
> Vin 6149 plus 2418, 3633, 5030, 16473, 17086
> Google earth: 52°25'17.66"N, 21° 1'58.40"E
> 
> --------------------------------------------------
> From: "birdwell77095" <birdwells@...>
> Sent: Friday, July 13, 2012 1:20 PM
> To: <dmcnews@xxxxxxxxxxxxxxx>
> Subject: [DML] RPM Drop When turning on AC
> 
> > How much should the RPMs drop when turning on my AC? A friend's car only 
> > has a minimal drop, maybe 50 RPMs. My car seems to drop 200-300 RPMs as if 
> > there is a large load on the engine. Bad electrical contacts? Not fully 
> > charged? It blows cold so it seems to be fully charged.
> >
> > Shannon
> > VIN 16113
> >
> >
> >
> > ------------------------------------
> >
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> >
> >
> >
>




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