I've been searching for information on the FEH A/C system, just to satisfy my own curiosity. I haven't removed the large cover over the engine to look, but I'm pretty sure the compressor for max A/C and the defroster is powered off of the ICE like any other car, since the ICE has to be running, even if it's just at an idle. What I want to know is how the normal A/C and recirculated settings work. Is it a separate compressor, a completely separate A/C system or thermo-electric and is it powered of the 12V or 330V system? Last time I used it on an hour and a half drive, it didn't seem to affect gas mileage at all. I actually got better gas mileage than the previous time I took the same trip.

 

You're right. The compressor is run off of the ICE. What happens in the white settings is that the fans will continue but the compressor will shut off along with the ICE (red settings keep the ICE running so the compressor never shuts down). It's the same compressor.

 

You're thinking waaaaaay too advanced here. Normal A/C brings intake air from the outside of the vehcile... recirculated intakes air from INSIDE the vehicle. Thats all it means. If its 100F out recirc will be alot cooler since you aren't trying to cool 100F air.... you are cooling cabin air again.

Nothing changes with the A/C compressor no thermo-electric... nothing

Max A/C locks it so the engine remains on as long as the compressor is running. Normal and Recirculate make it so that the engine runs when it needs to.... and the A/C compressor is ONLY on when the ICE is on.

You are better off with A/C in recirculate mode than normal because in normal almost as soon as the compressor goes off you'll be blowing hot exterior air into the cabin..... in recirculate mode you'll be blowing around the cooler internal cabin air for a while until it warms up.

 

The difference may be that most modern day automotive A/C systems run the compressor all year around. Dehumidification during the cool/cold periods and cooling otherwise.

It's likely the FEH/MMH runs the compressor ONLY for cooling. So if the OAT was below your desired comfort level the Compressor might have been run to initially cool the cabin down from being closed up in the sun but not thereafter.

 

I'm not sure what you were saying, but the FEH uses the A/C compressor in defroster setting just like any other car. The compressor does not run below 32'F, but if it's 29 degrees outside, but due to a hot engine, the intake air is 32'F, it will run.

 

I'm not sure about the FEH, but in a typical car, the A/C compressor cycles on and off when the defrosters are running so it dehumidifies the air before blowing it on a cold windshield and fogging it worse.

Thanks for the info. It's all starting to make sense now.

 

Wasn't referring to the defrost/defog/demist mode.

 

I was curious about this last fall .....and as far as I can tell from the shop manual....the FEH PCM does not have an outside air temperature (OAT) input. It "infers" ambient air temperature from the intake air temperature - which it does measure and which is affected by engine compartment heat.