I wanted to see if I could get my AC a little colder than the cool it was. Added a can of 134 from AZ. Now blows super cold but compressor makes a racket and really is noisy when I crank car over 2000 RPM. The compressor also does not cycle on & off as it should, just stays on all the time? Any idea?

 

I think you have a leak if you hear a hissing noise along with the higher rpms. What you could try is having someone rev the engine for you, while you go near the AC compressor and see if the hissing is coming from there.

 

You are probably overcharged if it sounds like one of those flywheel toy cars you had as a kid and varies with RPM. BTW the hissing noise is a pressure relief valve trying to save your overcharged system!!

Do it right... get some guages or take it to a professional - even with guages (and a temperature range) 134a is tricky for even that most mechanically inclined. Don't wait you'll blow your compressor!!

I would at least bleed some off at the low side valve (engine/compresser off or you will lose compressor oil) before I ran it more.