Refusing to activate air-conditioning for fear of increasing fuel consumption tends to be a false economy. Early systems were especially powerhungry and could increase fuel use by up to 10%. While car manufacturers and their suppliers have improved air-conditioning efficiency, inexpensive small cars with low-powered engines remain the most affected. However, more expensive, largerengined vehicles, especially those equipped with climate control, are fitted usually with variable displacement compressors, many of which run continually (although some types are fitted with clutches) that vary power use with demand via an internal solenoid that acts upon a swash plate. On long journeys, especially those that involve high speeds, the air-conditioning element of the HVAC system should have a negligible impact on fuel use and engine power. In any case, not using the airconditioning system at least once a fortnight risks gas escaping, which exits via shrinking internal rubber seals that dry-out as a result of not being lubricated by a working system. Long periods of inactivity can also damage the compressor, with subsequent repair bills eclipsing the fuel saved.