Originally Posted by Madeinsheffield
I'd like to ask a question, if the ac button is pressed which helps with demisting, does this affect fuel consumption as the thermostat isn't set to be on colder than the outside temperature, therefore am I correct in thinking the refrigeration unit isn't running so consumption shouldn't be affected like it would using ac on a hot day.
I'm sure somebody out there either has the knowledge or done some testing.
When the air conditioning/snowflake button is on, the compressor is engaged. Refrigeration is active and the air will be heated again (after being cooled) to achieve requested temperature (or actually, to get near to the requested temperature, within a 'fudge factor' that takes into account several variables.)
I have tested the fuel economy of several other cars when the air conditioning is engaged or disengaged - my conclusion is that the economy difference is too small to measure reliably.
For the original poster on this thread, I suggest to choose the lowest temperature (LO?) on both sides and then turn the fan speed down. It can help to open a window, just by a little, to help the flow of air into the cabin from the vents. That's what I find works best in summer when it otherwise seems to enjoy adding warm air to the cold air (probably the fudge factor).
In winter, cooling followed by heating is not a total waste since the action of cooling the air also removes humidity. Plus, the compressor should be run for a few minutes at least once a month to maintain seals in the system (it states this in the handbook).
The compressor will not run if the outside air temp is below about 3 degrees. That might cause it to cycle on and off if the temperature is around 3 degrees C.