Incidents of sudden, severe condensation the talk of owners’ social media feed.

INSTANCES of Atto 3 cars suddenly fogging up with condensation while being driven, sometimes in alarming circumstances, should be reconciled by an over-the-air software patch and an advisory, the distributor believes.

The matter affecting the best-selling model - and holder of the current New Zealand Car of the Year title - from the Chinese electric car specialist has been reported by dozens of New Zealand owners on a Facebook page.

Some suggest Auckland-based BYD New Zealand has been trying to effect a fix for several months.

There are mixed feelings whether a recent ‘hard’ update of the ventilation system that required cars to be taken to dealerships made the issue better or worse.

Since then, BYD New Zealand has relayed an over-the-air software patch - which the car can accept as it is configured with Wifi-connectivity - that some seem to question.

BYD NZ national manager Warren Willmot, pictured below on day of receiving the NZ COTY trophy from the NZ Motoring Writers’ Guild, is confident the OTA is a good fix but says the matter is being investigated further.

“All updates will be communicated to our customers via official channels.”

A husband and wife who experienced the fogging with their own Atto 3 and one they hired in the South Island recently says the matter has become the talk of the private on-line group.

The shared experiences of dozens of drivers build a picture of the issue only having arisen since autumn and worsening in full winter.

The car only released late last year and the owners were early adopters. They’d never had an issue with the ventilation in the warm months, but everything changed from autumn and became steadily worse in winter.

In the past month it was triggering on fine as well as wet and cold days, and not only when the car is being driven, but also when it was parked and unoccupied.

Other potential causes of leaks - something wet being left in the car or rain leaking in - have been checked and eliminated as causes. And they’ve seen three unoccupied Atto 3s parked together, on a fine and dry day - but one was fogged.

The husband said he was driving at 100km on a cold misty day with the heating on and air directed to the windscreen when it nonetheless suddenly fogged up.

“It happened so fast … the windows were just dripping.” He took a moment to realise what had happened as it was a foggy day. “It was a scare as I had my young grandson in the car.”

They had the issue again with a hired Atto 3 that had just 900 kilometres on the clock they took from Christchurch and say their experiences correlate with reports on the BYD Atto 3 NZ group, which has 4200 members.

Posts there cite issues arising when driving on the Auckland and Transmission Gully motorways.

“Someone who said they were halfway across a bridge when they suddenly lost all visibility, that would have been a heart-stopper,” the husband said.

Atto 3 is among a number of electric cars that favour a heat pump to effect air conditioning - the advantage being low energy draw which, in turn, enhances the car’s range. It compresses refrigerant under high pressure and the heat produced warms flowing cold air.

BYD says its system has the industry’s first direct cooling and heating system, which has the potential to increase the thermal efficiency by up to 20 percent in winter.

Air conditioning pumps out dry air to remove water vapour and inhibit the reaction that causes fog.

The couple who spoke to MotoringNZ.com said they understood that glass could mist up on cold, humid and rainy days and how . keeping the air conditioning would normally counter that.

BYD had notified them about the hard update but, because of the differing opinions within the Facebook group about the effectiveness of that action, the couple elected not to do it.

However, they did try the OTA patch and believe it to be effective as their car has since behaved.

Willmot said the OTA had gone to all NZ owners. BYD has not shared their specific thoughts about the reason for the issue but says the OTA contains “several system updates.”

Willmot also offered that “on some customer cars, the air conditioning system is defaulting to ‘automatic air con mode’.

“If drivers experience windshield fogging, they are advised to hit the defrost button on the centre console, which will clear the windscreen quickly.”

The convenor of the Atto 3 owners’ page was invited to comment. Nothing has been forthcoming.