What do you mean by "refrigerant blowing off"? Is it venting to the atmosphere???
If So. You may have a restriction somewhere, such as a clogged orifice. This would cause the suction to drop and (if you keep adding refrigerant) the discharge pressure to skyrocket. If you have this condition be very careful. The relief doesn't open till about 500psi!!! At that pressure all kinds of bad things can happen! At that pressure the compressor would cause the engine to "stutter" because it becomes very hard to pull. If a hose blows off, or the condenser or lines rupture, you could be seriously injured.
Generally with a clogged orifice the low pressure switch on the suction accumulator will cycle the compressor clutch off. If that's defective or as been by-passed then pressure can run uncontrolled. If excess refrigerant is added or air/non-condensables are in the system pressures will be higher as well.
I suspect that by hooking a refrigerant can to the low side you are raising the suction pressure, which causes the low pressure switch to close, which runs the compressor until the relief blows off! Very very dangerous!
Don't have much to go on here so I would suggest you take it to an AC shop to be checked out!
DIY is not always the best plan.
The AC shop may charge you some for their expertise but it'll be a lot cheaper than a visit to the ER........ just saying.
Last edited by CatFish; July 21st 2019 6:55 pm.