<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by V70SAM:<BR><B>Does anyone know if the compressor works at different levels based on outside temp and commanded temp inside?<P>In simple terms, does the compressor either come on or off, and no in between levels of use? <P>I ask this because I wonder if keeping the a/c on at all times is a good thing, even when the outside temp is cold and you are commanding warm temps from the selector knobs?<P>Sam</B><HR></BLOCKQUOTE><P>Depends on the outside temps. But yes, typically the a/c runs and the air-blend door mixes warm air from the heater core with the cool a/c air to get the interior temp just right. a/c will be shut off when the outside air inlet temp is cool enough to buck the heat from the heater core.<P>Also, when outside temps are above freezing and if the windshield defroster is turned on, the A/C will kick in to dehumidify the air blown onto the windshield. (My T-bird auto climate control did this, I noticed the S60's did, too) Of course, cold air doesn't feel good or help to de-fog the window, so warm air is added from the heater core to raise the temps. <P>The trouble is, the instant you turn off the a/c the water that was condensed on the a/c evaporator core will now turn into gas and then condense on the window and block your view!! So you have to leave the system on defrost and leave the a/c on to keep the water in the evaporator core. It's a pain, I don't like wasting the gasoline to run the a/c when it's 40 degrees outside.