"Adrian" wrote in message
...
Peter Campbell Smith gurgled happily,
sounding much like they were saying:

I don't know the real answer either, but a car with aircon is carrying
the extra weight around all year

Mebbe 10-15kg - or about 1% of the average car's kerb weight.

and there must also be a slight extra drag on the engine all year as
the belt to the aircon compressor is turning all the time.

Yes, but when the compressor's clutch is disengaged, it really is very
little extra load.


In the case of my car a single belt drives a number of auxiliaries,
including the a/c compressor, and there are at least two idler and
tensioning pulleys as well. The a/c compressor with its clutch disengaged is
equivalent to an idler pulley. These days cars tend to have a/c designed in,
rather than as an optional extra, so it is difficult to asess the effect it
has on fuel consumption. On my car there is a link to the engine management
system to cut out the a/c compressor at full throttle so that all power is
available for acceleration. I once drove a small-engined rental car in a
tropical climate where an essential part of every overtaking manouevre was
to switch off the a/c manually so there would be enough power available!

D A Stocks