Workshops could gain valuable business by reminding customers of the importance of regularly having their car’s air-conditioning unit serviced if they want to avoid the substantial risk of its failure.

Data collated by Warranty Direct shows that one in 20 claims for vehicle defects now relates to air conditioning systems.

On average, its says owners will be presented with a bill for £444.68, making the air-con compressor the fourth most expensive single repair after automatic gearbox, turbo-charger and engine. For as little as a tenth of that cost, car owners can submit their systems to suitably equipped and trained garages for an annual health check.

Vehicles aged 48-60 months are particularly at risk, accounting for 44% of air-con claims handled by the warranty specialist. Cars less than four years old make up only 14% of the failures.

“Too many people treat air-con as a fit and forget option,” says Warranty Direct’s managing director Duncan McClure Fisher. “Units need regular use and regular servicing to help prevent expensive breakdowns.”

Warranty Direct published an online Reliability Index, using data collated from its claims, to give consumers an indication of the likelihood of major component failure on common models of used cars.

The company was recently awarded a Crystal Mark by the Plain English Campaign for the clarity of the wording used in its insurance policies.