When I saw it the first time I thought maybe I was just tired and seeing things, or maybe the vehicle is having a weird day of strange behavior. But sure enough, on my way to work again this morning, the engine was shutting off when I was coming to a stop! The climate control was set to the one that splits heat and defrost... definitely a red setting. The defroster was doing a good job of de-fogging the windows too, so I'm pretty sure the a/c compressor was running. Did I just get lucky somehow, or do you think there might be something wrong with it? Air temperature has been below zero if that makes a difference.

 

The A/C actually ISN'T running.... Mine is doing it too now. If the outside air temperature is too low the A/C compressor isn't used.

Two reasons...
1) the air is already drier than a dessert once you heat it up. you don't need the A/C [this is why many people humidify their homes in the winter after heating the cold air up the relative humidity is 20% or less. Warm air holds more water, the cold air after its warmed contains the same amount of water, but the RH drops],
2) if you did manage to wring some water out it would freeze out in the evaporator and you'd have a block of ice.

Fortuantely the computer in these things seems to be smart enough that if the compressor isn't being used...then it allows the engine to shut down in the red settings!!!! Of course since this happens at temps so cold its not funny... our gas mileage still goes pretty south.

Someone else in one of the other threads has already reported what you've noticed.

 

The A/C compressor does not run under 32'F.

The red setting ( defrost ) is not SUPPOSED to let the engine turn off.
But I'm starting to hear others report what you are saying.
This may be a programming "update" for 2007.
Defrost always keeps my 2005 on, unless ABS happens, then the engine shuts down with defrost on.
Or maybe it has been possible all along, but when it's really cold, the engine won't shut off anyway, so maybe I just haven't had good luck.

 

My 06 FEH has been shutting off the ICE with the defroster in the red zone lately also. I live in upstate NY & it has been right near zeroº here lately.

Although the engine is certainly cycling on & off, with it this cold my gas mileage still sucks anyway(I'm getting about 8mpg less than I did in the Summer)

~John

 

At least for me, when it is too cold for the A/C to run, it is too cold for the ICE to shut down for other reasons.

 

Mines an '06..... You have to have the engine REALLY REALLY warmed up... its not going to happen unless you've been driving a bit, and it doesn't stay off for long

It might be an update for the '06 instead of the '07's

 

My 06 acts the same way.

~John

 

The A/C cooling evaporator, by design, will NEVER be chilled low enough to freeze the condensate on its surfaces. So at ~33F and below the A/c compressor circuit is disabled completely.

Actually anytime the A/C is running for only airflow dehumidification it is truly a wildcard as to whether or not it will be functional for that purpose, strictly dependent on local climatic conditions.

 

Yep... we understood that. What is interesting is that the FEH control unit recognizes this and won't bother to lock the engine on all the time as it will to run the compressor normally. It sees that the compressor is not running and will shut down the ICE normally.

 

Now that we've finally had a few days with temperatures in the teens here in the DC area, I can confirm that on my 2007 FEH (AWD), the ICE WILL shut down, at least for a few moments at a time, with the heater set in the defrost settings.