Automotive Air Conditioning Information Forum

I just want to say that I'm not a new member, but it's been years since I've been on this forum so I re-registered. Also, this isn't a question of whether using the 12oz. cans of refrigerant is a proper way of filling a system. Just curious as to how the full contents gets pulled into the system? It seems at first, when the can is full, it would have higher pressure than the low side (30-40 PSI). But as the can empties, it's pressure would be below the low side pressure, yet it continues to be pulled in till it's empty.

Good question, actually.
If the can is at an ambient of 70°, then the PT chart tells us the pressure in the can is 71 psi, which is about double the low side gauge pressure.
Now, it makes no difference whether the can is full, half full, quarter full, etc, the pressure will remain at 71 psi. So the can pressure is unrelated to how full it is. This is called vapor pressure and it is a chemical characteristic of that particular refrigerant in a confined space

Thank you for the explanation. It seams reasonable, but when you initially release the contents of the can, the gauge indicates the higher pressure. The gauge should be at the pressure in the can all the way till the can is empty, which is not the case.

Not sure what is your point. If using those little plastic gauges attached to a short hose like you get in a parts store, they are not accurate anyway.
If the lowest pressure you see is over 35, then the refrigerant will migrate to the low side circuit. There is no magical force involved.

Suggest Tim close this.

Also. whenever I have used cans, they don't empty. That's why California has a deposit on the cans for return and catching unused R134. The cans sold there have a special adapter that holds that excess R134 in. Only about 3/4 of the can even gets into the system. It's a big waste compared to a bottle.

Thank you tbirdtbird for responding to my question.