ONE of the UK's leading leasing firms is warning drivers to keep their air conditioning on or face costly repair bills. Lex Vehicle Leasing says unless drivers run the air conditioning for at least an hour a week the systems can stop working, resulting in bills of up to £1,000. Jamie Wiseman, maintenance manager, said: 'If a system is not used for a few months, it is likely to suffer from reduced performance or it might just grind to a halt.'