I recently purchased a used Honda Accord and failed to check if the a/c (R134A) worked or not. Unfortunately, the a/c doesn't work at all. I'm not sure if the compressor is turning on, but when i hit the ac button with the car idling, the car vibrates quite a bit, and the engine rpms drop. The ac only blows hot air. I just recently checked the freon pressure by connecting a guage to the low side port and came up with a reading up 25 pounds. (Should i add more freon?)

Can you give me any advice on what to do?