AC Gauge High Side Needle Fluctuating Wildly

[BigJim1]

I will try this again. 2003 Pathfinder LE, AC not blowing cool. Today I hooked the AC gauges up to the truck and after engine was at operating temps, the engine revved to 2500 rpm, the high side needle went crazy. It was fluctuating so fast I couldn't see the needle. I took a video of it and it slowed the needle down where I could see it fluctuating between 235 too 300.

Once I slowed the rpms back to idle the needle settled down again. Any one have any suggestions what is causing this? I would post photos but I can't figure it out on this forum.

[AlanAZ]

Many other vehicles, my Camry for one, say to read manifold gauges with the engine at a constant 1,500 rpm, BUT the FSM for the Pathfinder/QX4, say to read the gauges with the engine at idle. Could give you chapter and verse on the Camry, but have not needed to top up the QX, but I did note this important difference. The pressures do changes a lot between when the compressor is engaged and not, FSMs typically give the settings/conditions to keep the compressor always engaged. (And I really wish the QX had a sight glass like the Camry does, all vehicles should.)

If I can make a risk assessment: brakes, suspension, much engine work you can do over with minimal extra cost. It's $100 - 120 to service an a/c professionally, it's 10 times that much to replace the compressor if you get it catastrophically wrong. Just saying.