I'm hoping to get some inputs from 2009 owners as to if the new model has this same characteristic in VERY HOT weather.

In very hot weather (over 90 degrees or so), my 2008 AWD FEH will raise the RPMs about 500 if the A/C button is selected. If I deselect the A/C, the RPMs go back to normal range.

For example, at about 40 MPH, level terrain, the RPMs are at about 1500 WITHOUT THE A/C SWITCH. If I turn on the A/C, the RPMs jump to 2000 or so. I saw this happen a couple of weeks ago.

I have always found this frustrating, but we had a thread a while back in which some owners in Los Vegas had the same symptoms. It really doesn't make much sense unless the engineers were programming for more power when the A/C would be used harder.

 

One problem is engine load and that 2.3L Atkinson at low RPM. Add ethanol and the problem grows with the A/C compressor and you need more torque and RPM to hold your speed. The '09 2.5L handles ethanol much better and has just the right amount of power to handle the load at low RPM.

It's getting hot here in So. FL and my A/C is kicking in to cool the battery now. I still kept my low RPM and averaged over 54mpg today. I'm at 56.2mpg on my navi for the tank near 700 miles and I expect a fill-up tomorrow which may be a record tank for me at around 54mpg with E10. I'd be lucky to get 44mpg this time of year on E10 in my '05 FEH. I'm impressed with FMC!

GaryG

 

Blame the e/CVT for this.

A CVT allows the engine to run at the most appropriate RPM for a given road and roadspeed, generating just "barely" enough HP/torque to move the vehicle along at a given speed. Add in the extra load of the A/C compressor along with the possibility that the compressor must run at a higher rotational speed to attain the most optimal efficiency and you get a "bump" in engine RPM.

 

My wife's '08 FEH is having the exact same issue. So are you telling me we should use gas that has NO ethanol or what?

 

No, I don't think it is ethanol, it is some kind of programming in the car computer. I have found no way around it. The response you read is assuming it was lack of power, but I personally think it is Ford programming (OK, maybe the pre-2009 is adjusted to the 2.4L engine, but in any case I don't think it is automatic based on the fuel - it is in the CPU).

 

The local Ford dealer found some code in the AC system but when they checked the AC system there was no code directly in there. They said they would need the car for some time to pinpoint the problem. That must be some way of them saying the economy is bad and we are going to milk the pot for everything you have! I HATE dealers!

 

It is not the fuel.
It is becuase of the A/C and this is perfectly normal.

The A/C takes 2-3 horsepower to run.
At idle the egine is only making about 10 horsepower.
Thus, that A/C is about 20% extra load!

Totally normal.
Now you start to see why A/C lowers MPG so much...
But you won't notice this much at highway speeds.

HTH,
-John

 

It may be normal for a 2008, but I doubt it. My 2005 does not behave like this at all. I am one month into 4 straight months of virtually non-stop A/C use and have not seen this kind of behavior. Today, driving at 45MPH with cruise and A/C on (Tav was 91.4F so the A/C would be on even if I didn't turn it on) the RPM varied from about 1490 to 1505. The fact that the RPM changes when you turn the A/C on or off means your battery temp is not requiring A/C. There is no way the A/C should require an extra 500 RPM at any point in the 2.3L power curve. The only time I see higher RPMs like that is when the SoC is below 40%. In fact, my MPG with A/C if SoC is 53% is much higher than my MPG with no A/C and an SoC <50% and normal charging.

If other 2008 drivers see this behavior then I wouldn't worry. But it sounds to me like you might have a compressor going south or some other issue in the A/C system.

 

I STILL haven't gotten any feedback from 2009 FEH owners. Have you ever seen this "high RPM" behavior? The outside temp needs to be above about 97 F.

 

"..there is no way the A/C should........."

In the olden days the A/C compressor displacement HAD to be high enough to adequately cool the cabin in most typical circumstances enountered even with the engine idling. All the idle control system or ECU had to do when the A/C clutch was engaged was to open the throttle plate slightly.

Nowadays we have variable displacement A/C compressors that only run in the highest displacement mode under the worse cooling conditions. And even then the displacement can, will be automatically reduced as engine RPM rises.

Then we have the newest Toyota HSD systems that use a variable frequency AC inverter to drive the compressor at whatever speed is rerquired to "carry" the cooling load. It isn't so much a matter of ICE HP needed to run the A/C compressor, but the higher ICE RPM rate needed to have a relatively low displacement A/C compressor pump enough volume.

Think of your FEH's e/CVT system as a variable speed AC inverter for driving the A/C compressor. The compressor displacement can be "sized" for maximum efficiency, to only handle the maximum cooling load with the engine "racing".

And it very well could be that the above technique was only arrived at, for FE purposes, for the later, '08+ FEH models.