Fuel consumption is only one thing that suffers. No one has mentioned the hit on performance:D. Anyone car to throw a few figures around on this issue?

Car air con compressors consume about 5 KW (6 HP) of energy when running. This equates to about 2 to 3mpg on your average fuel consumption. Obviously the smaller the engine the greater effect.

Some cars will cut out the compressor when the throttle pedal is buried in the carpet. This obviously frees up a few extra horses.

The point is that you never get anything for nothing. Any extra load on the engine whether it be the A/C compressor or even lights for that matter will cause extra fuel to be used.

My previous Mk 1 Octy Tdi 90 averaged 59 mpg over 110,000 miles and the manual A/C caused the mpg to drop by 10% and I could feel that it needed more throttle when it was switched on. My 4X4 140 diesel is doing about 44 mpg brim-to-brim with the Climate Control on Econ compared with 42 mpg with the CC set to 20 degrees. So the mpg is reduced by about 5% which indicates that in Econ the compressor maybe isn't switched off as some posters have alluded to.

So the mpg is reduced by about 5% which indicates that in Econ the compressor maybe isn't switched off as some posters have alluded to.

When the climatronic is in ECON mode it backs the compressor off to something like <5% capacity to keep the compressor shaft seal oiled thus preventing refrigerant leaks. But this must absorb more power than a compressor with an electromagnetic clutch.

The ECON button's description is spot on as it isn't actually disconnecting the compressor from the drive belt.