Four out of five new cars sold in the UK now come fitted with air conditioning, yet the likelihood of an expensive failure has jumped 55% over the past 18 months.

According to research by independent automotive warranty specialist, Warranty Direct, 1 in 20 claims are now air con-related with the cost of repair running into the hundreds, or even thousands.

Analysis shows that the most susceptible vehicles are those aged four years old.

Vehicles in months 48-60 of their life accounted for more than 44% of claims handled by the firm. Vehicles younger than four years accounted for just 14% of air-con claims.

On average, owners will be presented with a bill of £444.68, making the air-con unit the fourth most expensive item to repair after the automatic gearbox, turbocharger and engine.

Although the air con units on some models appear less reliable than others on paper – for example, the Volvo 850 reports a failure rate of 37% and the Ford Galaxy nearly 27% – too many vehicle owners fail to see the importance of servicing, Warranty Direct said.

“Too many people treat air con as a fit and forget option,” said a spokesman. “Units need regular use and regular servicing to help prevent expensive breakdowns.”

An annual health check and service should cost around £40 from an independent specialist, he added.