Refrigerant gauge read in the red or overfilled?

I had an A/C compressor installed may of 2024. Last year 2025 spring came and It wasn't blowing cold air. They refilled it with coolant with dye. This year no cold air and I took it back. They said the lines to the evaporated were leaking. They quoted between $500-$1500 to repair. He suggested I just refill Freon yearly due to the age of the car $175. I went out and bought Freon with the gauge. I was able to attach it the proper lower line and the gauge read in the red or overfilled. I released the pressure by pulling the trigger but the gauge went back to the red. I checked the compressor and the clutch was engaged and it was running. I had the engine running and A/C on high. I want to refill coolant but what would cause to gauge to read overfilled? I don't want to damage the system anymore than it already is.