1998 Mustang AC pressure gauge fluctuates and hits red when filling

ForeverDrivin

So my car stopped putting out cold are about a month ago. I realized something was wrong and not wanting to burn out my A/C clutch or just break the compressor in general, I've tried to keep the A/C off.
I went to get a refrigerant refill kit and when I read the pressure, it fluctuated up and down. Did some research and found that if it's fluctuating, it's low. However, when I actually started refilling it immediately hit red on the gauge, whether compressor was engaged or not. The pressure fluctuates as the compressor engages and disengage. Here is a video: https://drive.google.com/file/d/16Ln0tAtL12fGy464ZrV1jmjVnQrH5vJS/view?usp=sharing

I say when the compressor is and isn't engaged for reference. I should note that RPM drops and power loss happens exactly when the pressure drops and the compressor is engaged. Engine visibly shakes and compressor sounds like it's struggling when on.

Any help is appreciated, thanks!

Mr_Shiftright

Those refill kit gauges are wildly inaccurate, and relying on them could cause damage. For AC, you should really have a professional shop slap their gauges on it to see what's what. If you over-charge, you are surely going to damage the compressor and then you're into a lot more $$$ than a recharge fee from a pro.