I have been known to place the can in a small bucket of hot water. That is how I over pressurized the system! Turning the can sideways or upside down for a few seconds will allow the fluid in the can to flow into the system. The fluid will turn to gas rapidly once in the plumbing. Pouring too much fluid in can screw up the system if done too rapidly. Remember, the warmer it gets outside, the more R134a expands and increases the pressure. That is why Florida cars have 2oz less fluid than northern cars.

Do not bypass the pressostat for a long period of time. The compressor will fail if the system is too low on pressure and forced to run.

I usually run mine at 60psi, engine off pressure. If you are using a can with a builtin gauge, it is probably reading too high. They err on the low side.

Klaus
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Always willing to listen, just not able to take direction.