Idle, Alternator, Compressor Problems

when ac or heater is on, compressor clicks, fan starts, revs drop too far below normal which makes engine rumble, then compressor clicks off, revs return to normal....this process repeats every 3-4 seconds until ac turned off or heat moved back to cold. also, if i have lights on or press my window switches the revs drop.

ive tested the alternator and that is fine (volts/amps are what they should be until ac or heater is put on then they drop to below the correct volts/amps)

car drives fine unless you have ac or heater on, then the low revs process (as stated above) starts and if i am driving then slow the car, the revs drop and the car rumbles until i pull away again.

have new icv, tbs, air filter, no vacuum leaks, air con re-charged last week.

am i correct in thinking that when the compressor clicks on, it ISNT meant to click off again with 3-4 seconds if the car is stationery? it should click on and only click off when i turn off the ac or heater?

also, on the opposite end of my icv to where the wiring connects, there is a small hexagonal hole. what is this for? adjusting the idle?