I noticed today a problem with the dual fans when the ac is on runs about 30 seconds then cuts off...it stays off for about 20 seconds and comes back on, runs about 30 seconds then cuts off and over and over the same thing, when the fan is off the head pressure goes high.... so what is causing this to cut the fan off and on?

Cooling not "cooking"

sounds like either a circuit breaker for the fans, a relay that’* failing(there is prob like 3 relays, only the relay related to ac should be activated. )
try swapping the cooling fan relay for ac with a similar relay for something else and see if it fixes. If it doesn’t, I’d looks t wiring or the fans themselves but if your relay moves the problem, say a low speed fan now operated in the same way, then it nails that relay

The condenser fans only work when the high side pressure gets up to about 185-190 then the needle starts falling and the fans cut off, then when the pressure gets up to 185-190 the fans come on and the process starts all over again.

If anyone has a schematic of the fan circuit on a 2000 Monte Carlo SS.......

It works just like OldsManiac1990 said...You verified it with your pressure readings and fan operation. I have the diagrams but they are not necessary.

I've checked all the other things and it looks like it is leaking down and the only place I can find is on the evaporator...... Does the entire dash have to be removed to replace the evaporator on a 2000 Monte Carlo SS??

If you use dye you'll see it come out the evap drain if it'* leaking there. I'd make sure because you are going to need to pull that side of the dash pretty well out.