If it's blowing refrigerant out something is clogged. Also, there may be a problem with your high pressure cutoff switch(it should cut the compressor off long before refrigerant loss.
Have somebody put a set of gauges on it and try to get a running pressure on both the high and low pressure ports. With the system off, your static (non running) pressure should be between 110 and 150 PSI(this varies by temperature, you can NOT judge proper system charge by static pressure. The only thing you can tell is: if the static pressure is below about 100PSI the system is radically low, as in no liquid refrigerant is in the system. If the static high and low pressure readings are not the same, there is a bad restriction in the system.
I can't give you accurate numbers, as both running and static pressures change with outside air temp and inside vehicle temperature. (This is why AC is a PITA by the way,.. ) but generally:
Turn the AC on and watch the gauges. The high pressure gauge will rise above 200, and the low pressure gauge will drop to around 45.
If the high pressure gauge doesn't reach 200 and the low pressure gauge drops below 40psi, the system is low on refrigerant. if the low side pressure drops below about 30psi, the low pressure cutoff switch will shut the compressor off. This "short-cycling" is a sign of low refrigerant.
If the low pressure gauge drops below 40PSI, and the high side pressure continues to climb above 200, there is a restriction. If it's a bad restriction, all the refrigerant in the system gets trapped in the condenser lines. Then either the high side pressure will continue to climb until the high pressure cutoff shuts down the compressor, or the low pressure cutoff will shut off the compressor because there's no refrigerant left in the low pressure lines. If this happens, the pressure will slowly equalize and the compressor will kick back on again, and repeat the cycle.
The most likely restriction (clog) is the orifice tube or accumulator.
The orifice tube is in the high pressure line between the condenser coil and the connection to the evaporator coil. You replace the whole line
(Link to napaonline - orifice tube)
The accumulator might(ok,.. will) get clogged if any kind of leak sealant has ever been put in the system.
(Link to napaonline - accumulator)
