Why Re-Charge your air conditioning system?
Your cars air conditioning system will lose 10-15% of its refrigerant every year, this means that after 3 years your system (if not serviced) can be down by as much as 45% of its refrigerant. This makes the compressor run for longer therefore reducing your MPG.
Whats more when will it let you down?
Just when you need it the most, on those really hot days ! If the system is low on charge it will not be able to achieve the low temperatures required to sufficiently cool the interior of your car. In addition to this your AC system lubricates itself by the refrigerant carrying the oil around as it circulates, therefore insufficient gas equals insufficient lubrication and possibly compressor failure.