What surprises me is that it happens only during transients from idling to high-speed operation. I don't know if reving the engine in place will do the same thing; I should check. It is worse at lower ambient temperatures, or so it seems.

I put too much in it before the last time the temperature hit these kind of highs, and starting the compressor immediately put the high-side into the upper twenties. I removed about eight ounces at that time, but have since put about two back in. Perhaps another ounce or two will fix it up.

With only one kg of refridgerant in the entire system, I should expect some severe sensitivity to a few ounces high or low.