1996 Idle increase/decrease with possible hissing noise!

My wife and I just bought my parents 1996 Ford Explorer with 62K miles on it. I have never had a Ford before and do not know if what I am hearing under the hood is normal or not. When the vehicle is in park and idling, the idle speed seems to fluctuate, (almost sounds as if someone were shifting the vehicle from park to drive, park to drive, etc.). When the fluctuation occurs there is a click coming from the air conditioning pump; the front portion of the pulley that is attached to the A/C pump stops rotating, even though the pulley is being driven by the belt; when that front portion of the pulley starts rotating again, that is when the click is heard and the idle speed fluctuates. Also, when you have the hood up and the vehicle is idling, you can hear a constant high pitch hiss, (kind of sounds like a gas turban engine!). The vehicle is a 1996 4X4 V6 4.0L; sure hope someone out there can tell me if this is abnormal or just the nature of the beast.

Thanks all,
Jason

Turn off the heater and A/C switch and see if problem goes away. If the switch is on the compressor cycles on and off to help condition the air so the windows inside of the car will not condense. This is normal. However, if your A/C is turned on and the compressor cycles on and off, this may indicate that the freon charge is low. As to the sound, you may want to spray some belt dressing and listen if the sound changes. You may want to replace the serpentine belt. Also check that all of the vacuum hoses are seated properly.

Your right! I turned off the heater, and the A/C stopped cycling. I guess I'm just not use to the operation of this SUV yet. I already replaced the belt about a week ago, but I will check the vacuum hoses.

Thanks!
Jason