Gas Mileage myths or facts?

[curtis73]

Originally Posted by SaabJohan

15 hp is a bit much, but up to 10 hp is possible.

You've evidently never done much work with Frigidaire A6 compressors 17 hp is common for some of their bigger ones, and some larger 70's American cars use TWO of them.

[Moppie]

Originally Posted by SaabJohan

15 hp is a bit much, but up to 10 hp is possible.

In a small modern car yes, but I know of some early American cars that had compressors that needed as much as 70hp to drive them, thats more power than my 1st car produced.
Of course A/C technology has changed a lot since then

[SaabJohan]

Originally Posted by cody_e

Newer vehicles (at least 1998) stil do that. They let the comrpessor spin every 15 seconds or so to keep the bearings from going out in the compressor itself.

Newer cars are equipped with electronic throttles and variable displacement A/C compressors. With the help of variable displacement the compressors can be connected to the engine most of the time the compressor is used. Heat removal is controled by changing the displacement. Power loss is compensated with help of the electronic throttle. The pressure in the A/C system is used to calculate how large the compensation must be. A variable displacement compressor isn't turned on and off so many timed but when it is, the electronic throttle and ignition timing is used to make the connection/disconnection smoother.

Older cars with constant displacement compressors tend to do turn the compressor on and off several times to control the heat removal. During full load they were usually turned off. No or some compensation was used. When compensation was used this was to allow for a smooth connection/disconnection.

Originally Posted by curtis73

You've evidently never done much work with Frigidaire A6 compressors 17 hp is common for some of their bigger ones, and some larger 70's American cars use TWO of them.

A modern compressor like a Sanden SD-7 series takes about 8 hp or less. This is enough for a large modern car.