Quick question about A/C - Heat

That does not mean that the compressor is on, only that it is enabled in case it is needed to dehumidify the cabin air.

 

As the compressor speed is controlled by the computer it only runs as fast as it needs to to get the job done, so it wouldn't need to run at full speed to dehumidify the air if it was cold out.

This is unlike a conventional car air conditioner where the compressor speed is determined by engine speed and a valve allows the system to work at different compressor speeds but with variable cooling again dependant on engine speed and the AC cycles on and off to control temperature. This uses more power than necessary and is not able to cool at its peak when idling causing temperature variations.

The Prius air conditioning is like the inverter reverse cycle air conditioners manufacturers rave about and you pay more for, for your home. Except the Prius uses engine heat to heat the cabin.

 

Actually, the Prius air conditioner compressor would be locked out in cold temps anyway. The PAG oil isn't rated for cold temp operation. However, if you have heated parking, then the compressor could still run until either the pressure switch tripped it, or the temp sensor shut it down

For my home, I have the A/C programmed to lock-out at temps colder than +55 F. If you don't have a heated compressor blanket, operation in temps colder than that will result in short compressor life

My FJ Cruiser is programmed to run the compressor whenever the selector is in Defrost or Defrost/Floor. Since I have heated parking, that means the compressor is on, and I have no control over it. The interior will get bloody cold until the system senses the bitter cold outdoor temps and the compressor is locked out

At least the Prius I can manaully disable the compressor. With the FJ, I just went into the master fuse box and pulled the compressor relay. Problem solved

 

I've heard to think of the A/C light in the Prius as auto climate, instead of air conditioning.

 

I thought something similar! I was thinking they meant air conditioning as in it "conditioned" the "air" to whatever temp the user wanted. "air conditioning" could technically mean either hot or cold... or maybe I'm just a huge dork with too much time on my hands.

 

The A/C light simply indicates that by pressing that button (or by proxy through the AUTO button) you have granted the car permission to run the compressor as it sees fit.