Is it true?

Depends on each vehicle. For some the extra load of the aircon helps improve engine breaking marginally but on others they have an idle up feature that would make it worse. Billy Goat track is certainly not that steep to worry about it unless you're driving something geared very high like a Subaru for example.
Cheers Craig............

Most vehicles have an ilde up for air con, but after 1000rpm you do get extra engine braking. I tend to use it as an engine brake more on the road when towing my boat. Years ago I had a Rocky diesel that could decend very steep hills in fourth with the air with out touching the brakes. But modern air con units are much more efficent, and modern vehicles are geared much higher with low ficton engines.
Cheers Pete

Mark,

If you think that it is rough coming down, try going up.

I was there a few weeks ago and some of the petrol vehicles in the convey had to turn the air con off just to make sure that they did not stall or lose power.

Years ago when the idle up on the air con was not an option we use to run the air con on petrol vehicles and even run with high beam and driving lights on just to try and slow the vehicle. It did help but with the gearing being high, even in low range, first gear, the vehicle still felt that it was racing down hill.

Nothing beats a big 6cyl diesel with a manual Toyota gear box for going down hills slow.

Wayne

On a certain level I can understand the theory but on another level I don't.

If I use my TD Troopy as an example it'd actually go down the hill faster with the air conditioning on.

The reason for that is the idle up solenoid mentioned by a couple of people above.

As Wayne has mentioned, the best way to go down a hill real slow is with a big diesel six, low range and a manual gearbox.

I guess it depends on the age and the configuration of the vehicle.

Geoff

It works fantastically well on my Kia. A/C off and I have to keep touching the brakes to keep it dead slow. Switch the A/C on and I can put both feet on the floor on the steepest grade.

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