I had the P/S fluid level going down in the reseroir, and looked under the vehicle to see where it was leaking, and there was what is termed the "pressure switch", which I was told the function of it was to disengage the A/C compressor when turning at maximum turns to allow more engine power to the P/S pump. My question is this the function of the switch, and the reason for it to malfunction at only 70.000 miles?? Defective part??

Well lets see 2002 with 70,000 miles. You did a lot of low speed turning. A round the town van..City driving is a little harder on a car than hwy driving. Or could have been defective.