No expert here but on my Onan Emerald 4000 I adjust the frequency without a load to about 119-120 VAC. Once the load is applied the governor should adjust the engine as needed. Might try it without load and see what it does when you turn on the A/C. Also there are pivot points on the generator that you can add a drop of oil to in case it is hanging up. I usually see a drop off to about 115 VAC when I turn on the A/C. Hz may fluctuate a little but no more than 2 -3 HZ continuously. Momentarily the HZ may fluctuate even more but that could just be noise on the AC.