Need Troubleshooting Procedures for A/C on B14

[Darren]

Car: 97 SE-R

Mileage: 112,000

Mods: Stock with the exception of the K&N Air Filter

Issue: A/C is blowing warm when the engine RPM is over 4k.  The blower is on
but starts vibrating heavily.  At this point, it stops moving air.  After a
while, it comes back on again and becomes cold, but the air is moist.  I
can't tell, due to the noise of the moving air, if the vibration is still
there when the A/C is working correctly.

I would like to know the best way to start troubleshooting

To date, I have tried:

1. Turning the recirculate on and off - no effect
2. Changing the vent position from floor, to top, to defrost - no effect

I took it to a local Nissan dealer and they were unable to duplicate the
problem.  Instead, they gave me a copy of a TSB that stated the thermostat
may fail when the car has been sitting in the sun. However, the A/C is
usually fine when I first start up the car, irreguardless of the sun.
Any suggestions would be greatly appreciated!

Thanks,