Originally Posted by stevedebi

If I read your suggestion correctly, you are suggesting TWO compressors, one for when the ICE is running and one for electric only? Interesting, though it would be expensive to have two compressors.

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It is the people who wish to change Ford's careful design

I wish, truly, that we could see Ford's careful design prior to beancounter "optimization".

who are "grasping at straws", as you put it. I am telling them that it is not that simple.

I am simply pointing out that a hybrid system is far more complex, and the parts interact more closely, than a conventional drivetrain.

Ford certainly knew they could go to an electric compressor, yet they did not, even with the 2009 (so far as we know). So the car we bought is designed to use a mechanical compressor. That means that the computers (especially) are designed to compensate for the engine driving the compressor, NOT for an electrical compressor. This particular thread is listing an interesting part of the programming, namely that at temperatures above around 98F, the CPU directs the engine to add around 500 RPM when the A/C is engaged.

As a software engineer, it irks me that people think they can simply swap stuff out and have the vehicle simply work the same as before.

Maybe you should spend a bit more time with some hardware design engineers.

How many software engineers does it take to change out a light bulb....??

None, that's a hardware engineering task...

These vehicles are very precisely computerized, and any such change would require adjustments to the CPU programming -

So, you're saying that were I to swap out ALL of the incandescent light bulbs, interior, stop/tail/turn/street/parking, for much more efficient LEDs (10:1), use 35W hi/lo HIDs for headlights, the software might need to be changed to compensate for the reduced electrical load...??


for the engine, and possibly for other components, to compensate for the ELECTRIC compressor - which draws FAR more AMPS than the factory sound system.

I wouldn't be so quick to jump to that conclusion were I you. An electrically driven compressor, driven via an energy efficient variable frequency AC inverter as in the Prius/RXh/HH, can be run, operated, at whatever pumping rate just barely meets the cooling needs of the passenger cabin. That allows the evaporator outflow "target" temperature to be set just a few degrees below your temperature setpoint.

Whereas an engine belt driven system as currently used in the FEH/MMH series is of the "bang-bang" on/off cycling type(***) and with an UNLIMITED refrigerant metering system, target temperature of the evaporator outflow is ALWAYS <35F. That's why the FEH/MMH still uses the reheat/remix air temperature regulation method, giving two reasons why the ICE must be run with A/C on.

*** Exception: many newer AC systems use a variable displacement, "swash plate" A/C compressor so the engine belt driven compressor pumping rate can be adjusted independently of engine RPM. Sort of an individual CVT for the A/C compressor.

Originally Posted by wwest

I'm not saying, nor proposing, that there will not be times that the A/C is the EXCLUSIVE reason for seemingly inordinantly high ICE RPMs, just that sometimes you might see a high rate for other reasons or combined reasons.