a/c issues

I have a 2004 echo and my a/c has been intermittently working for the last year, it cycles on and off every 30 seconds one day then it works fine the next. The other day it just quit and hasn't come on since. I have checked all the wiring,fuses and all the sensors. I bypassed the clutch relay and checked the pressures for the refridgerant both high and low are good. All my relays tested good aswell. I have a wiring diagram and I can't seem to get a ground to energize both the fan relay and clutch relay, I know it should get it through the a/c amp some how.
Just wondering if anyone has had problems with the a/c amplifier or if they know how to test it? or what inputs are needed to make it give the ground to energize the relays. also wondering if the a/c amp would be the same through all the earlier ECHO's cause I have a friend who owns a 2001 and he said he would let me swap amplifiers to see if it would fix, just don't know if it is compatable.