1998 Mustang AC Pressure fluctuating and in red when filled

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!

You need a qualified air con shop. These systems are not really do it yourself items .

I’m just looking around to see if anyone knows of an easy fix. I’m not keeping this engine for too much longer and am not gonna spend tons of money on it. However, did not know if someone has had this problem before and it turned out to be an easy fix.

It sounds to me like the A/C system is overcharged, and/or has air/non-condensibles in the system. What needs to be done is: recover all of the refrigerant to a disposal tank, change the accumulator-drier, pressure test the system with compressed nitrogen, properly evacuate, and recharge by weight with new refrigerant. If you do not understand how to do all this, and don’t own all of the necessary tools and equipment, then you’re going to have to take it to a shop or live without the A/C.