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Is the condenser/aux fan operating properly? Not having airflow across the condenser could surely cause a 400 lb reading on the high side. Your car has a pressure operated fan switch (unlike a W123=thermal fan switch), so the fan should come on almost immediately after the compressor clutch is energized. Don't overlook dirt and leaves in the condenser (behind the shroud), they will cause a lack of airflow as well. Another potential cause could be a stuck expansion valve. They are cheap enough that you can replace it just for piece of mind. If everything above is in order, I would be looking for a blockage somewhere (as others have said). It is so easy for the novice to just add refrigerant, and not start at the beginning. If the refrigerant is low or completely gone, there is obviously a leak somewhere. The first thing to do after recovering the remaining refrigerant, is to leak check with a dry gas. Any leak(s) need to be fixed before proceeding. It is also a good idea (as mentioned) to flush the system (evaporator, condenser, hoses), and then replace the receiver/drier, and add the proper amount of oil. Just adding refrigerant and an arbitrary amount of oil to a system is not good. Too much or to little is not good. Again, the best way is to start from scratch (leak check, flush, drier etc). That way you know that everything is the way it is supposed to be from the start.....Rich
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