Problem: A/C compressor - pump oil and refrigerant all over the engine

Question: Got a great one for the curious professional. 1971 GMC C2500 Kustom; 3/4 ton pickup; 2-whl drive; automatic transmisson; 402cc engine. Problem: A/C compressor. System inop. Event#1 - replace comp/receiver-dryer/evaporator coil. Pull a vacuum and charge - cools fine down to 36 degrees. 10 hours into operation some clutch seal or gasket fails and distributes pump oil and refrigerant all over the engine compartment. In fact the clutch assembly basically exploded. Okay, return the warranteed part and start over. Again, install goes well - cools to high 30''s but after 10-15hrs of operation the compressor begins to throw a mix of oil and refrigerant across the engine hood and compartment. Can''t really identify from where it originates. By now we involve a shop - what''s up? They say on GM only there is an adjustment (pressure) somewhere within the system that has to be dialed down when converting from r12 to r134a - makes sense - too Answer: I have seen this before. The oil that is spraying everywhere is coming from the pressure relief valve located on the compressor. It is supposed to do this when the pressure is too high to avoid the compressor from actually blowing up. The problem you are having is a failed high pressure switch. Yes it is that simple. On the high side of the system there is a high pressure switch and it is supposed to shut off the compressor when the pressure gets to a certain point and then once it drops, it allows the compressor to kick back in. P.S. there is no adjustment for dialing down the pressure. Just replace the high pressure switch and all will be fine.